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Boat building advice?: Building foam core dingy


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Hi,

I bought a ripple tender kit: https://www.spiriteddesigns.com.au/ripple_tenders1

The kit came with all of the pieces CNC cut from 10mm 80kg foam (Divinycell H80).  The kit also comes with temporary MDF frames to build the boat on. (Only the first picture is mine, the other photos I found on the net)

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There are two options for building:
1.The foam can be temporarily tacked to the frames, tape the seams then hand laminated. Let it cure, remove from MDF frame and repeat for the interior.
2. Or laminate the foam pieces on a flat table, then tack to the frame and tape the exterior pieces, remove from the frame, tape interior pieces
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I have done a bit of vacuuming bagging and will probably go with option 2.  Laminate the foam in a vacuum bag on a flat table, then proceed with the build over temporary MDF frame.
 
My main concern is although most of the panels look pretty straight, some of the panels will need to bend to fit the frames (at the bows and forward part of the bridge deck).  Do you think that once both sides of the foam is laminated, it will be able to bend to the frame?  On the panels that need to bend the most (bow sections and forward bridge deck) maybe just laminate the inside, then lay up the exterior side once bent in place on the frame?
 
I've been using West System because its easy to get, but would like to use a different epoxy as the West is too viscus thus difficult to wet out fabric.  I was thinking about trying Proset but not sure which of their laminating resins to use (medium vs low viscosity)?  Any other epoxy recommendations?
 
I bought 40 meters of 320gsm of carbon plain weave from Alibaba (because it was cheap!).  Do you think Chinese carbon is ok to use?  Maybe I'll do a little test laminate to make sure its not cotton dyed black!
 
I'd like to make the dingy as light as possible because it will be hanging in davits. Also it's much easier to carry, pull on the beach, and hoist on deck a light dingy than a heavy one!
 
Anyone have any insights that might help in the building process?
 
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21 minutes ago, mrybas said:

n the panels that need to bend the most (bow sections and forward bridge deck) maybe just laminate the inside, then lay up the exterior side once bent in place on the frame?

This. Both sides glassed might be too stiff to make the bends easily. 

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There is no way you will bend the panels with a layer of carbon each side.

I would laminate the inside on a table and then fit  the panels to the frame.

Once taped I would remove any screws and fill the holes. The panels then should remain in place while you laminate and vac the outside laminate. 

If there is an issue bending to fit to the frame then heat the panels. I found 105degC to be the ideal temp for the M80 foam.

It is a shame they didn't supply female frames. Then you could fit the foam before laminating and vac the inside laminate, remove and vac the outside. That was how I built Mad Hatter and it worked great.

I have used hundreds of litres of West building cedar strip hulls for a 32ft cat and several other resins on other projects. Mad Hatter was built with

Gurit. I much prefer the Gurit resin.

I think the Chinese carbon would be ok for that project.

What was the laminate specified with the kit?

 

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5 hours ago, The Mad Hatter said:

What was the laminate specified with the kit?

This from the Ripple Tender designer:

I have had a response from the head engineer from ATL and the advice is:

 

300gm carbon plain weave as main laminate each side of the foam with additional 450gm double bias tapes or drops where required. This can be e-glass and applied anywhere where impact can be expected. These areas are:

 

Hull bottoms

Top of bridge deck 

Foredeck

Floor area in hulls 

 

The hull bottoms and internal floor area is covered when the tapes are applied so this adequate as standard. The bridge and foredeck will need additional laminate however an extra 300gm may suffice.

 

Remember that the tapes for the joins are additional to the main laminate and should be applied as specified in the plans.

 

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It's "how light do you dare" - puncture resistance is the main issue with foam core dinghies. They're plenty strong enough for wave/bending loads etc. but drag it up a rocky beach and your 300 gm plain weave carbon better be treated very carefully.

For E-glass 450 minimum, 600 for durability on the outside.

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This is one of those projects where glass is a better choice over carbon. The boat needs to withstand impact. Weight will not be an issue when you poke a hole thru your cheap Alibaba carbon weave. I would have gone with Zonkers 450/600 layup. If being able to pickup your dinghy with one hand is your goal...go carbon. If its occasionally beaching your new ride...go glass. 

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1 hour ago, Zonker said:

It's "how light do you dare" - puncture resistance is the main issue with foam core dinghies. They're plenty strong enough for wave/bending loads etc. but drag it up a rocky beach and your 300 gm plain weave carbon better be treated very carefully.

For E-glass 450 minimum, 600 for durability on the outside.

 

35 minutes ago, CaptainAhab said:

This is one of those projects where glass is a better choice over carbon. The boat needs to withstand impact. Weight will not be an issue when you poke a hole thru your cheap Alibaba carbon weave. I would have gone with Zonkers 450/600 layup. If being able to pickup your dinghy with one hand is your goal...go carbon. If its occasionally beaching your new ride...go glass. 

Does anyone know anything about Innegra? My brother's girlfriend has an SUP made with a carbon/Innegra blend.  Its very ding resistant (much more so than a glass or carbon board) and also pretty light.

Maybe its worth adding some Innegra to the high impact areas (keels, deck, etc)? http://www.innegratech.com/videos

Or doing away with the Alibaba carbon and using Carbon/Innegra blend?

Or see if I can find some S-glass?

Or just live with the extra weight of E-glass?

Maybe I'll put some keel guards to protect while pulling up a beach?  I plan on adding Beach Master wheels, so won't be dragging the dingy around too much.

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These are foam/glass/carbon tenders built in NZ.  They have a big foam bumper with sunbrella cover for impacts and coming along side the big boat. https://octenders.co.nz/#foto-principal.jpg-nggid0279-ngg0dyn-240x160x100-00f0w010c011r110f110r010t010.jpg.65bd5a791191f2eee69cef554876c5c9.jpg

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I did a flats skiff project recently and the client had heard about Innegra and I checked it out. Seems to have great potential but is hard to find. A sales guy said that the mill that makes most of it in the states had some technical issues and production had stopped. There is an old cotton textile mill in S. Alabama that was bought for production of Innegra for use in armour such as vests and helicopter bellies and blades. It is very close to the Army helo skunk works in Ft Rucker which is home to Army Aviation. Here is a helo solo certificate.

Image result for army helicopter school alabama

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I'd like to keep the dingy as light as possible because I don't want all that weight directly over the stern.  But at the same time, I don't want a boat thats going to need fiberglass repairs after every trip to the dingy dock!  What would be the best compromise between weight savings and durability?

 

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Innegra = olefin 

That means polypro or polyethylene. The polyethylene can be strong (Dyneema) but neither are likely to be stiff (carbon and lesser extent glass).  It probably gives you thickness for little weight because its density is so low but ..

Found the TDS buried a bit here:  http://docs.wixstatic.com/ugd/9836da_8db14832f50a463892a035be260a773c.pdf

- Elongation is 9.5-10% That is very floppy. Carbon is around 1%, E glass around 5%

- density = 0.84. Probably more polypro than polyethylene

Thus, a tough ductile fabric that isn't very stiff. For a paddleboard the carbon provides all the strength, this adds durability. It used to be fashionable to sheath wood / ply boats in xynole (polyester). Stretchy stuff too.

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I have also looked into Basalt fiber in the interest of abrasion resistance. After all in is made from remelted lava (magma) rock and spun into fiber which seems quite compatable with E or S glass. Hard as a rock?

This would be good on chines and keels on such a dinghy.

Volcano Wrap, Basalt Fiber, 2" x 50 ft.

https://www.zoro.com/techflex-inc-volcano-wrap-basalt-fiber-2-x-50-ft-vwn200ba50/i/G8064135/

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The Innegra reads like a modern replacement for carbon/kevlar cloth. Nothing special going on here other than the modern weave. It could be much better than the kevlar. Anything is better than straight carbon for impact. Interestingly, I just watched this destructive testing of carbon mtn bikes versus aluminum. The carbon bikes are almost indestructible. The really need a point load to locally damage the layup. Those tubes are very thin on the bikes built in the last 5 years.  Seriously impressive.

 

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Tack the foam to the formers and then laminate it all in one.

You will save weight/time/filler by not taping the joints.

No need to vac bag - one layer of biax goes on easily with a squeegee. Peel ply and a stiff brush will get the excess resin out out and give a good finish that will need little fairing thickness

Waste of money using carbon - you can save weight by building this way and have a stronger boat

A nice way to build!

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6 hours ago, The Mad Hatter said:

Just in case you have not done the numbers   _   The weight diff between a layup of 450/600 glass and 320/320 carbon would be around 5kg. 

Ie.  13 compared to 18 kg if the hull surface area was 6 sq m.

 

How do you arrive at the math above?  This is a weight calculation for 12 sq m. of 320 gsm carbon and resin (2 sides of 6 sq m. hull) VS 6 sq m. 450 gsm glass and resin (inside hull) + 600 gsm glass and resin (outside hull)?  

 

 

The dingy's LOA is 3.6m

Total surface are of the whole boat is roughly 17 sq/m.

Its 6 sheets of Divinycell at 2.4m x 1.2m

 

 

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2 hours ago, teamvmg said:

Tack the foam to the formers and then laminate it all in one.

You will save weight/time/filler by not taping the joints.

No need to vac bag - one layer of biax goes on easily with a squeegee. Peel ply and a stiff brush will get the excess resin out out and give a good finish that will need little fairing thickness

Waste of money using carbon - you can save weight by building this way and have a stronger boat

A nice way to build!

Building this way does sound much simpler!  

The designer did specifically mention that the tapes are in addition to the main laminate.  Do you think the tapes are not required if the hull is laminated as one piece vs taping the panels together?

From Craig Schionning:

I have had a response from the head engineer from ATL and the advice is:

 

300gm carbon plain weave as main laminate each side of the foam with additional 450gm double bias tapes or drops where required. This can be e-glass and applied anywhere where impact can be expected. These areas are:

 

Hull bottoms

Top of bridge deck 

Foredeck

Floor area in hulls 

 

The hull bottoms and internal floor area is covered when the tapes are applied so this adequate as standard. The bridge and foredeck will need additional laminate however an extra 300gm may suffice.

 

Remember that the tapes for the joins are additional to the main laminate and should be applied as specified in the plans.

 

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You are right, the website shows a photo of tapes going onto a foam hull before the skin. I would have thought that the shape provides the strength at these points. 

Stick to the plan or there is no point in paying for them [To quote Farrier!]

I like the tender. Would suit my Catana 381!  No heavier than an inflatable with an aluminium floor either

Will you add some sort of fender/bumper around the gunwal?

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13 hours ago, CaptainAhab said:

The Innegra reads like a modern replacement for carbon/kevlar cloth. Nothing special going on here other than the modern weave. It could be much better than the kevlar. Anything is better than straight carbon for impact. Interestingly, I just watched this destructive testing of carbon mtn bikes versus aluminum. The carbon bikes are almost indestructible. The really need a point load to locally damage the layup. Those tubes are very thin on the bikes built in the last 5 years.  Seriously impressive.

 

I'd love to see an equivalent Titanium frame added to that test.

 

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The bottom(s) of that boat are narrow, so the weight of a heavier layup only on the bottom is reduced.  If there's a rocky beach in your future, I'd be thinking maybe 2000 gsm total.  The bottom is only about 1 M^2, so so the whole bottom layup would be about 4Kg.  Kevlar skidplate on the edge would be worthwhile, too.

 

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  • 6 months later...

After much delay, I finally got started on the dingy building project last week.  I’ve been vac bagging with 300gsm carbon with 6oz e-glass (I think that’s 200gsm?).  The bulkhead, transom, and flat pieces have all been laminated both sides.  Currently working on laminating the inside of the hull sections that will bend over the frames.

 

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For hull bottoms I’ll reinforce with carbon/Innegra for potential impacts.

Hull sides will have with closed cell foam padding with sunbrella cover (ala Offshore Tenders) or a thicker version of seaDek.

Interior (seat, floor, other horizontal surfaces likely to be walked on) will have seadek.

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I am very interested to hear your progress, as I have been thinking about a Ripple. 

I presently have a Walker Bay superlite 270, which is a foam-core ‘glass RIB. It comes in at something like 72 pounds. It’s been a good dink, if wet ride. I mentioned this bc that would be my weight goal for a build.

Did I miss where you said the expected weight to be?

PS. Dridek is heavy. And so is cc foam, esp if you’re going to cover it. My advice: Be a Nazi about weight, esp for all the trouble to build.

pps. Nice Crowther

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For an all around fender on my dinghy I just used pool noodles. Took around 20metres of line to lace them to the gunwales but they work great at projecting

the side of my tri when pulling along side and cost very little.

The have lasted 2 years in the sun and I may need to replace them in another couple of years. 

I'll admit the closed cell foam and sumbrella may look a little more stylish but it would be a lot more work. Both alternatives  are doing the same job.

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11 minutes ago, The Mad Hatter said:

For an all around fender on my dinghy I just used pool noodles. Took around 20metres of line to lace them to the gunwales but they work great at projecting

the side of my tri when pulling along side and cost very little.

The have lasted 2 years in the sun and I may need to replace them in another couple of years. 

I'll admit the closed cell foam and sumbrella may look a little more stylish but it would be a lot more work. Both alternatives  are doing the same job.

I used pool noodles with some old sunbrella from an old tore up sail cover. I slit the pool noodle through one side on my table saw and wrapped the sunbrella around and poked the long edges into the slot. Did the same sort of tuck thing at the ends and then slipped it over the 1"x3/4" oak gunnel on my ply dinghy I had drilled 1/8" holes just under the sheer clamp about every 6 inches and ran nylon electrical zip ties through the holes and around the noodle finder and then cinched all the ties up snug enough that they buried about a half inch in the foam and it made a very professional looking and long serving fender for cheap.

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1 hour ago, Rasputin22 said:

I used pool noodles with some old sunbrella from an old tore up sail cover. I slit the pool noodle through one side on my table saw and wrapped the sunbrella around and poked the long edges into the slot. Did the same sort of tuck thing at the ends and then slipped it over the 1"x3/4" oak gunnel on my ply dinghy I had drilled 1/8" holes just under the sheer clamp about every 6 inches and ran nylon electrical zip ties through the holes and around the noodle finder and then cinched all the ties up snug enough that they buried about a half inch in the foam and it made a very professional looking and long serving fender for cheap.

When I have to replace them I think I'll do similar.

I lace the noodles without splitting them as I think it gives a slightly wider buffer which is handy when picking up the mooring and I put the dinghy between the main hull and float of the tri.   I will just sew up a canvas tube and slide them in. 

The cover is a nice touch.

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2 hours ago, Rasputin22 said:

I used pool noodles with some old sunbrella from an old tore up sail cover. I slit the pool noodle through one side on my table saw and wrapped the sunbrella around and poked the long edges into the slot. Did the same sort of tuck thing at the ends and then slipped it over the 1"x3/4" oak gunnel on my ply dinghy I had drilled 1/8" holes just under the sheer clamp about every 6 inches and ran nylon electrical zip ties through the holes and around the noodle finder and then cinched all the ties up snug enough that they buried about a half inch in the foam and it made a very professional looking and long serving fender for cheap.

Have any pictures?

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13 hours ago, mrybas said:

For now I have a 15 hp 2 stroke yamaha.  In the future, may look into electric propulsion.

I saw a similar catamaran dinghy that was quite fast with 6 hp and it seems like one advantage of the catamaran is that it could use less power. Even when loaded, it should move well at displacement speeds. Hard to imagine using a motor that weighed more than the dinghy. Keep the photos coming!

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10 hours ago, Russell Brown said:

I saw a similar catamaran dinghy that was quite fast with 6 hp and it seems like one advantage of the catamaran is that it could use less power. Even when loaded, it should move well at displacement speeds. Hard to imagine using a motor that weighed more than the dinghy. Keep the photos coming!

The boat is just under 14’ long.  I plan to use it to get to far away surf/kite/spear fishing spots while the big boat is safely anchored.  If the 15hp is more than enough power, I’m sure I could trade someone for a smaller outboard!

All of the flat pieces are laminated both sides and just finished the hull pieces that will bend on the frames (inside laminated). Trying to decide if it’s worth making a bigger table to bag the deck in one shot?

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I'd say don't bother. Just do it in 2 pieces. Rebate the foam (with a router) where the join will be and it will be easy to fair. No need to fair the underside of the joint, just the top visible surface.

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I got a chance to dry fit the pieces to the frames today.  They fit pretty well except where there’s a lot of direction change close to the bows.  I’m thinking about drilling small holes and dry stitching with leftover carbon scraps to pull the panels together (or maybe small zip ties)?

Next step is to bog the joints, sand joints, then tape.

 

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small zip ties work well. You can pull the joints together and them hold them with small dabs of thickened epoxy in the seams. then cut the zip ties

Or be lazy like me and just leave them in the laminate (taping inside seams first with zip tie closure on outside). Cut off outside part of zip tie but leave inside part under the tape. It will be noticable but to me a dinghy is a work boat not a work of art.

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A previous posting mentions the OC Tenders.  They seem like an interesting design in that they have a number of features of inflatables.  Seating on inflatables is frequently on the sides with everyone arranged around the boat.  Stepping into an inflatable is easy if one steps on the tubes because they are higher than the floor and very stable relative to the floor.  The OC tender seems to capture these features with the narrow decking on the sides of the hull.  The decking seems like it would also provide a great deal of stiffness.

  I have been reading another thread about hard dinks and nesting dinks.  The OC tender looks quite a bit like a stitch and glue skiff but these skiffs have seating that is in the middle of the boat and they use a lumber rail to provide stiffness.  Are there designs that have seating on the gunnels and/or put seating level with the gunnels? 

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  • 2 weeks later...
1 hour ago, Rasputin22 said:

That sounds like a good combo to me. Let us know how the innegra/carbon is for applying. Look at the Basalt fabrics for abrasion on the outside. Tough as rock and only slightly heavier. 

https://www.compositesworld.com/blog/post/the-still-promised-potential-of-basalt-fiber-composites

 

A buddy of mine is a surfboard shaper.  He 'glassed' a board with basalt fiber and it is significantly heavier than a standard e-glass job.  I have no experience with basalt, but maybe vac bagging would help?

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In that last picture, it looks like the panels have a lot of compound curvature. But in the picture previously, before all the seams were taped, it looked like typical single curvature developed shapes. i.e. shapes you could easily do with thin plywood.

Is the last picture just a trick of the light and I am seeing things?

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Any of this 'exotic' stuff would probably benefit from vacuum bagging. The Innegra especially since I think it would 'float' in epoxy resin and is pretty close to the decades old 'polypropelyne' cloth that was popular in England for ply boats and notorious for rising to the top when hand laminated. That may be why Innegra/basalt makes a good combination where the density of the Basalt acts as 'ballast' for the lighter than resin Innegra.

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7 hours ago, mrybas said:

The panel seams have all been filled and sanded.

 Now I have to try and figure out a flange at the gunnel for the vac bag to make a seal.  

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Maybe do a 120mm wide hand laminate with peelply all around the boat where you want to attach the bag, that will give you 50mm overlap and plenty of room for the tacky tape.

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3 hours ago, mrybas said:

Since the vac bag is only on the exterior, is there a risk of too much vacuum pressure 'oil canning' the foam between the frames?

The vacuum bag does not pull the core over the frames, it actually pulls the mold, in this case the core, towards the bag.

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10 hours ago, Zonker said:

In that last picture, it looks like the panels have a lot of compound curvature. But in the picture previously, before all the seams were taped, it looked like typical single curvature developed shapes. i.e. shapes you could easily do with thin plywood.

Is the last picture just a trick of the light and I am seeing things?

The piece that runs either side of the keel has compound curvature.  It took a lot of little blocks screwed to the next panel to hold the shape while filling the seams.  

7 hours ago, Major Tom said:

Maybe do a 120mm wide hand laminate with peelply all around the boat where you want to attach the bag, that will give you 50mm overlap and plenty of room for the tacky tape.

Good idea.  Sounds like the easiest and least risk of not making a good bag seal.  

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On 9/10/2019 at 7:05 AM, mrybas said:

The panel seams have all been filled and sanded.

 Now I have to try and figure out a flange at the gunnel for the vac bag to make a seal.  

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When building my tri I extended the foam 40mm past the frames and applied two coast of resin that was amine blush free and managed a good seal that way. Initially I put a layer of microlight and resin , once cured, I sanded and then a coat of resin over that but found out as the project progressed the filler was not needed as two coats of resin were sufficient to fill the exposed cells of the corecell. foam. I would wait until the first coat went tacky before applying the second coat.  With an amine blush free resin I could apply the tacky tape straight over the cured resin. I also had a couple places where I put tacky tape over peel ply but found I got a much better seal if I lightly sanded the peel ply and put a coat of resin (that did not produce amine blush) where the tacky tape needed to go. Of course the resin had to cure before applying the tacky tape. So the tacky tape makes a much better seal over the smooth resin than it does over the raw surface created by the peel ply . I could always get  vacuum of get around 25 inches of mercury when applying tacky tape over the cured smooth resin surface.   

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Pulled the boat off the frames today.  I need to get two scales to get a proper weight, but I’d guess it’s less than 75lb as is.  Still need to tape interior, add deck, outboard pad, fair, prime, paint and add fenders.  Hopefully finish weight is under 120lb. Boat is 13’ loa 4’8” beam.

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  • 1 month later...

Looks sinister-cool in black, but a burning hot bugger to live with though. You going white? That’s a big dink for less than the weight of a man! 

We ski behind a 4.3m alu rib with an old 20hp and half chewed prop - albeit needing two skis for deep water starts for my 75kgs - with two same-sized guys in the rib as driver and observer. Once dropped to a slalom, the driver needs a bit of opposite lock to counter a decent carve and keep running straight. :)  I bet you could ski with your 15hp if you can do two-ski beach starts (deckchair!). And certainly kneeboarding/biscuit etc.

Your boat will zip like a skinned cat!!

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I went for a quick test ride with a 2 stroke 15 hp.  The boat moves along quite well in displacement mode with maybe 25% throttle.
When I try and go faster, a heavy stream of water sprays into the boat between the transom and outboard.  The plans call for a rubber gaitor that would fit around the outboard leg, which I still need to fit.  I’m also wondering if I also need a long shaft outboard?  I’d also like to switch to a lighter outboard if possible, but I’d like to be able to plane with 700 lb payload (4 people and surf/kite/spear gear).

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It looks like you just need a fairing from the upper cavitation plate to the level of the underwing. Something like a skeg that's attached to the underwing that splits the water for the fat part of the leg. It could be rough & ready shaped foam. The boat looks great!

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I'd be curious about the idea of the rubber gaiter. Not quite sure how to visualise it. I think Russell is correct about the wedge fairing. Google Livingston dinghies. Small cat dinghies used to built around here with that sort of thing. Take pictures if you get the gaiter sorted out!

You'll need 15 HP for 4 adults for sure

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Whether you did the rubber thing or not, the fairing would reduce drag. An outboard is supposed to be behind the transom all the way down to the upper cavitation plate. The leg above there is shaped like a club, and goes through the water like a club. The Grasshopper had a succession of different fairings that were attached to the leg, not the boat (that was an extra-long shaft). I found that the fairing needed to extend at least 10" forward of the leg to be sharp enough to split the water with minimum fuss. Your boat seems perfect for a simple foam fairing attached to the underwing.

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Are you using a Doel Fin? When I built my first tunnel hull dinghy that was much like what you have come up with, those plastic molded things were not on the market yet. I just shaped one up in 1/2" ply carefully foiled using the ply lams to shape and fit it to the cavitation plate. Then I adjusted the height of the motor mount of the transom so that the water coming off the top of the tunnel hit right below the fin. Cleaned things up without hanging another shape in the tunnel to further compress flow. Boat got on the plane quicker and would stay on the plane longer when slowing down and increased payload capacity to still get up on plane. I figure I got a couple of extra knots top end speed. The foil needs to be operating at a 2-3 deg angle to the waterflow coming off the hull so play with the pins in the transom mount to dial that in.

 

Image result for dolphin for outboard

 

 

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  • 2 months later...

My buddy just finished spraying the Awlgrip.  Now I just need to find  a long shaft outboard.  I want to find a 10-15hp two stroke, but they are hard to come by Stateside.  I may be rowing until I get to the Caribbean!

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  • 2 weeks later...

I got to take the dingy for a test spin yesterday when we pulled into VA Beach to wait for weather to go around Hatteras.

5 guys (1000 lb) with a borrowed 6hp 4 stroke.   The waterline dropped quite a bit, but the bridge deck was clear of the water.  With very little throttle the boat would do 4-5 knots.  At full throttle the boat would do about 7 knots.  Not enough power to get the boat on plane.

I plan on picking up a 15hp long shaft two stroke once in the Bahamas or Caribbean.

The boat is pretty stable when passengers are moving around/getting on or off from the boat, but not as stable as an inflatable.

I still haven’t had a chance to weigh the boat, but it’s much easier to lift into the davits that the old 11’ inflatable.  It used to be a 2 person job (2:1 tackle) .  I can lift this boat into the davits solo.

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  • 3 weeks later...

I made some fenders by cutting 5” pool noodles in half and wrapping with Top Notch fabric.  They are attached to the hull with Velcro.
The fenders seem pretty stout, but only time will tell how the fabric and Velcro hold up to the dingy docks of the world!

 

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Those look great. I did the same with the the tunnel tender I built ages ago. You can easily drill holes that you can add additional tie wraps around the noodle and the fabric that will ensure that everything stays in place. Lots of additional flotation from those big noodles, I don't think I have every seen them that big a diameter.

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  • 3 months later...
On 2/5/2020 at 12:32 AM, Zonker said:

When you get it going fast, I would be very curious if it corners flat or leans outward in a turn like many cats.

It stays pretty flat when cornering at speed.

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I’ve used the dingy for several months now in the Bahamas and coming back up the East Coast.

I bought a Yamaha 2-stroke 15 when I got to the Bahamas and glad I waited....it’s the right motor for the job.

We use the boat for lots of ‘missions’ (Kitesurfing, surfing, spear fishing) often miles from where the big boat is anchored.  The foot wells have plenty of room to stack boards, kites, dive gear etc.  With 4 adults and gear the boat planes and the waterline hasn’t dropped too low.  This is probably the realistic weight hauling capacity while getting on plane and covering distance. You could weigh it down more if hauling a heavy load (fuel jugs, lots of people, etc) in a protected anchorage.  The boat sips fuel and seems to use significantly less than my old 9.5 AB RIB with the same motor.

The boat is very comfortable in chop, more so than a RIB.  The boat is dry up wind and down wind, but when there is a cross wind the spray wets the windward passengers.  It’s not a soaking spray, but enough to be annoying.  It’s tough to say if it’s more spray than a comparable size RIB without doing a side by side comparison, but I would guess it’s slightly wetter in a cross wind.  Possibly larger side fenders would be enough to act as spray deflectors. 

A bit more care needs to be taken when going to a dingy dock/davit loading vs an inflatable.  The cut in half pool fenders work well at fending off docks and tying along the side of the mother ship, although there are situations where composite hull on dock/other hard object can happen if not paying attention.  I guess this is the trade off for having a boat that will last a life time if looked after vs the 10yr life of an inflatable.

One other draw back is the boat seems harder to drag through the sand vs a heavier rib.  The two narrow hulls seem to plow through the sand.  I may try and install some beach wheels.


Do you think light weight composite catamaran tenders are a viable business?  I’m kicking around the idea of using what I leaned from this boat to build a plug then a mold to make a few for sale.  Anyone interested?

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Boat building is a really tough way to make a living. If you can keep it small it may work, but once you factor in labor, safety, shipping, warranty, liability, Coast Guard, etc, it can be a bad idea. We have looked into this a bunch because it makes so much sense to offer a production nesting dinghy, until you look at it closely.

I like the boat a lot and it seems like it should go somewhere. Would a kit with pre-skinned panels be a good idea? With the right designer (Rasputin & Zonker both come to mind) it could be a really smart kit. The panels could be CNC'd with taping rebates and all kinds of smart details. 

Just thinking out loud....

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11 minutes ago, Russell Brown said:

Boat building is a really tough way to make a living. If you can keep it small it may work, but once you factor in labor, safety, shipping, warranty, liability, Coast Guard, etc, it can be a bad idea. We have looked into this a bunch because it makes so much sense to offer a production nesting dinghy, until you look at it closely.

I like the boat a lot and it seems like it should go somewhere. Would a kit with pre-skinned panels be a good idea? With the right designer (Rasputin & Zonker both come to mind) it could be a really smart kit. The panels could be CNC'd with taping rebates and all kinds of smart details. 

Just thinking out loud....

Boat building being a rough business seems to be the common consensus from the couple people who I asked with experience.

I think the kit idea is great, but it would be a real nitch market.  I just don’t think there’s that many people that have the time or desire to build a boat, even if offered in a kit.

IF I did try building a few for sale I think I’m lucky in my personal situation.  The person who I’d partner with builds surfboards and has space in his warehouse to build boats.  We’d be doing all of the boat building ourselves at first to see if it’s a viable business. So there would be little cost beside material to build a mold and material for the boats.

My employment and other business are very flexible/seasonal.  So I wouldn’t be depending on the boat building to put food on the table per say.  However I don’t want to spend a bunch of time and money building 5 boats to get stuck with them/sell them at a loss.

I do think there is a market for an alternative to inflatable boats.  I think OC Tenders are starting to see some adoption by the cruising fleet and reviews by owners are mostly positive.  I just think a cat is a better boat for the job!

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The reason I'm so interested is I'm collaborating with a cruising friend who wants to get into the business of building composite foam/glass catamaran dinghies. I think there is a market - but it's similar to the OC tender which are not cheap. You're building in small volumes, bagging with core in a mold, etc. None of this is a cheap process compared to woven roving and a chopper gun and solid glass hulls like lots of glass dinghies.

He's built a prototype and leaning outboard in turns was his biggest complaint. There is very little literature on how cats behave in turns. Some lean in, some out, and some flat. Generally I'd be happy with cornering flat.

The Ripple tender was one of my design inspirations, along with Livingston dinghies (PNW solid glass cat dinghies) one of which my friend previously owned.


How have the fenders held up by the way after some months of steady use?

 

 

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Hi mrybas, your tender turned out great.

Did you get a finished weight , completed. After fairing, painting, fendes etc.

I am interested as I am about to start building my own, and finished weight can be so different from  calculated.

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1 hour ago, MRS OCTOPUS said:

Hi mrybas, your tender turned out great.

Did you get a finished weight , completed. After fairing, painting, fendes etc.

I am interested as I am about to start building my own, and finished weight can be so different from  calculated.

To be honest I have never weighed the boat.  After paint I would estimate the boat was 120ish pounds.  Then I added seadek, fenders, and keel guards.  I would estimate the boat at 150ish now.  I’m just finishing up a winter cruise in the Bahamas and heading back to the shop.  I have some small mods to make to the boat, so I’ll get an accurate weight while it’s in the shop.

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2 hours ago, Zonker said:

The reason I'm so interested is I'm collaborating with a cruising friend who wants to get into the business of building composite foam/glass catamaran dinghies. I think there is a market - but it's similar to the OC tender which are not cheap. You're building in small volumes, bagging with core in a mold, etc. None of this is a cheap process compared to woven roving and a chopper gun and solid glass hulls like lots of glass dinghies.

He's built a prototype and leaning outboard in turns was his biggest complaint. There is very little literature on how cats behave in turns. Some lean in, some out, and some flat. Generally I'd be happy with cornering flat.

The Ripple tender was one of my design inspirations, along with Livingston dinghies (PNW solid glass cat dinghies) one of which my friend previously owned.


How have the fenders held up by the way after some months of steady use?

 

 

My current boat was all bagged.  Foam/carbon,carbon/Innegra, glass.

The fenders have held up quite well.  Top Notch is a durable canvas material.  No rips or tears. A couple of pulls in the material when we tried to go up a rapid and aborted and ended up in some thick mangroves! 

 The foam does have some memory though and has a scallop where it’s lashed tightly to the davits while underway.  Though I do lash the dingy tight as hell while underway as we often see boat speeds in the upper teens!

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Here's my lock down project.

Same width and length as the inflatable but seems to be much bigger?

In these pics it weighed the same as the inflatable [45kg] but is gonna be a bit more after fairing and painting

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4 hours ago, teamvmg said:

The rebate for fendering is a pain to do but no point in a tender without a good fender!

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That fender rebate looks like a lot of work!  Good on ya.

What foam and laminate are you using?

You’re going to want to have a nice large diffuser on the bottom of the bridge deck just in front of the outboard shaft. With the transom extensions, water is funneled through the bridge deck and shot out the back like a fire hose.  Any water that hits the outboard leg is going up and into the boat.

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