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20+ Footer - Building in Hawaii


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Also designing a 32 foot boat for double handed racing.  Scaled up GP with specific details for DH racing. Looking at the competition; this is will be easy.

20 moved back into the shed today; needs a good cleaning inside and out. Hopefully it'll stay inside all winter and finally get finished!

Sorry WCB - those messages don't make it through my spam filters. The 20 is on the worklist finally to be completed and sailing this spring - only been 11 or so years . . . I'll start posting bui

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3 minutes ago, Chris in Santa Cruz, CA said:

no shit, did not know that, makes sense though, much cheaper and bomb proof

 

Yup - a bit deeper and a new bulb that weighs approx 150# more. Add the 2' extension on the transom and she's no slouch.

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5 hours ago, Chris in Santa Cruz, CA said:

no shit, did not know that, makes sense though, much cheaper and bomb proof

 

not *exactly* bomb proof. the ductile iron can be a bitch to keep properly encapsulated.

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14 hours ago, ryley said:

not *exactly* bomb proof. the ductile iron can be a bitch to keep properly encapsulated.

my hotfoot 20 currently has the bottom and keep coated in red anti-fowling. I have no current intention to put it in a wetslip, what should the iron be encapsulated in?

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6 hours ago, Chris in Santa Cruz, CA said:

my hotfoot 20 currently has the bottom and keep coated in red anti-fowling. I have no current intention to put it in a wetslip, what should the iron be encapsulated in?

if you're dry sailing it, you're probably ok, just look for signs of rust. On the C-30/2's, they put a layer or two of glass around the iron, which is easily cut through by lobster pots and then the rust just blooms.

 

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1 hour ago, ryley said:

if you're dry sailing it, you're probably ok, just look for signs of rust. On the C-30/2's, they put a layer or two of glass around the iron, which is easily cut through by lobster pots and then the rust just blooms.

 

copy, thanks

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1 hour ago, ryley said:

if you're dry sailing it, you're probably ok, just look for signs of rust. On the C-30/2's, they put a layer or two of glass around the iron, which is easily cut through by lobster pots and then the rust just blooms.

 

holy cow did I typo that post!

kill the chickens!

my boat has country acreage, who knew

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19 minutes ago, Chris in Santa Cruz, CA said:

holy cow did I typo that post!

kill the chickens!

my boat has country acreage, who knew

I'm guessing the anti-fowling is working very well and there's nary a chicken to be seen around your boat ;)

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On 6/15/2021 at 8:02 AM, orca99 said:

Thanks for the clarification, and by the way - i love your GP26 design.

The SA comparison with the VX put you close to the SA of a SB20 - right? (46 m2 Spi, 27-28 m2 main/jib)

Also roughly same lenght and keelweight and your hull should be about 100 kg lighter.

You are certainly not at risk of being kicked out of the SA sportsboat forum with those specs, even if you call it a keelboat :)

I guess there are two ways to nirvana; a boat which will recover easily after a broach, or a design, which has small sails and very little tendencies to broach, at least if it is helmed by a person with a dinghy background. 

Will your 20 footer be fitted with lifelines? or foot straps?

If you sail with footstraps (like my VX), I estimate that 1 kg of (hard hiking) crew weight generate as much righting moment as about 3-4 kg of bulb weight. (we sail with with about 10 degree lean both up and downwind).

I guess with a heavier keel, i could carry marginally larger sails, but would it make the boat faster in average in a windy location?

The same question apply in reverse for your boat; would it be faster with smaller sails and less bulb weight?

Keel weight is not always a good thing. I still recall Jørgen Boisen Møller (olympic gold medalist) say that the Olympic Tempest sailed exactly like his Flying dutchman when the cockpit was filled with water. this is perhaps relevant as a modern sportsboat is faster than a Flying Dutchman dinghy in average, if the Portsmouth handicaps are to be believed.

Another poster believed a heavier, deeper keel is always faster/safer. If it was true, the VX with 60 kg keel and 1.3 m draft would have no chance against for example a M24. In reality they should be quite even both per Portsmouth and IRC handicaps.

In the hypothetical case that a sports boat could exceed the waterline limited speed even upwind, I am fairly certain that the optimum keel bulb weight is as low as possible, meaning whatever minimum weight is required to get you into the keelboat events in your area, and what you feel safe sailing with.

 

 

 

Thanks for your comments on my GP 26; the performance of that design has exceeded my expectations.

The GP 26 keel bulb mold ended up producing slightly heavy keels (+20kg), so we put a couple voids in the upper surface of the bulb to hit the 475kg maximum class bulb weight. Without the constraints of the GP 26 class, the most competitive boats have filled in these voids to boost the stability/speed. More bulb weight makes that boat faster.

And the 20 footer is a smaller version of the 26, with even more power; lighter structures, proportionally more sail, proportionally deeper keel fin, more topside flare to increase crew righting moment, and lower DISPL/L ratio.

And I want to sail this boat with a smaller/lighter crew, so extra crew is replaced with lead in the bulb. That lead doesn't take up space in the car, need a bed and meals, or fart. Less is more.

As keel weight decreases, the benefits of the lead reduces. IMO, designs with keels that require the crew to hop on the fin to come upright just aren't right. Why bother hauling the lead around? Just get rid of it and sail the boat like a dingy. Multihulls have figured out the best way to eliminate lead from the equation. 

 

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On 6/15/2021 at 3:17 PM, Chris in Santa Cruz, CA said:

One thing to consider here is that we found  that even though the first C30 keel spar was strong enough being 100% prepreg carbon fiber and had an optimized foil shape designed and built to ABS standards, it was too flexible torsionally and the bulb would swim and oscillate. We had to add more carbon to get it stiff enough to stop the swimming. Ended up overbuilt to ABS. It was interesting at the time to learn how ABS really did not address loads occurring at higher speeds of the modern planing hulls. Made me wonder how far into the safety factor some rudders and keep foils were actually going :)

Maybe there needs to be a C30 keel fin thread? Sounds like there's some issues there . . .

We've built 15 or so carbon GP 26 keel fins without an issue.

As I mentioned before, a carbon fin should be designed for stiffness, not strength. If your carbon fin is stiff enough not to bend too much, it'll be way too strong and twist won't be a problem. The 20's fin is designed similar to the GP 26 fin.

ABS rule has become obsolete for racing yachts over the past 10 years as the racing rules have switched to more modern scantling rules; GL, DNV, ISO.  There's a ton of data from designs produced in the era of ABS, so we often look at that rule see "what worked in the past". For appendages, the designs definitely exceed ABS requirements.

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  • 1 month later...

The 20 footer has had no attention the past month; worked on getting the Waarschip out of the shed and on it;s trailer for a regatta in Maine. Trailer bunks built and installed, bulb installed.

 

Final Planning.jpg

Thistle Bulb Install 1.jpg

Thistle Bulb Install 2.jpg

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Bonded the bunk laminate to the plywood with a couple layers of Carbon DB, and added a 4" wide strip where the bolts go to improved bearing strength and make a kind of backing plate so the washers won't compress the plywood. Found some 3/8" higher density EVA foam and doubled it up for the pads; expect it'll compress some by the time the boat gets to Maine.

Nobody at the yard just walks by this boat; spend more than a little time answering "what is it?".  

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On 8/1/2021 at 5:42 AM, Jim Donovan said:

 by the time the boat gets to Maine.

Nobody at the yard just walks by this boat; spend more than a little time answering "what is it?".  

and now I have questions...when? where? what yard?

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  • 4 weeks later...
On 8/6/2021 at 11:48 AM, mgs said:

and now I have questions...when? where? what yard?

Sorry but wrapped up with lots of stuff; we were in Maine to do the Eggemoggin Reach Race on Aug 7th. Boat went in the water Thursday noon, did the race on Saturday (3rd in class w/crappy rating) and back on the trailer Monday.

The race is run by Wooden Boat magazine and very well attended; maybe 150 boats?

I thought I'd experienced sailing around lobster/crap pots in the Chesapeake and Florida; Maine takes that to a whole new level! We snagged one at the top mark when we were dealing with a spinnaker SNAFU; had to back down in the middle of the set to clear the pot off the rudder. Fortunately there was almost no wind and it had no affect on our race.

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4 hours ago, Jim Donovan said:

Sorry but wrapped up with lots of stuff; we were in Maine to do the Eggemoggin Reach Race on Aug 7th. Boat went in the water Thursday noon, did the race on Saturday (3rd in class w/crappy rating) and back on the trailer Monday.

The race is run by Wooden Boat magazine and very well attended; maybe 150 boats?

I thought I'd experienced sailing around lobster/crap pots in the Chesapeake and Florida; Maine takes that to a whole new level! We snagged one at the top mark when we were dealing with a spinnaker SNAFU; had to back down in the middle of the set to clear the pot off the rudder. Fortunately there was almost no wind and it had no affect on our race.

I’d say it’s a haul getting to Brooklin from Vermont, but getting from Vermont to Maine alone (or t’other way round) is trip in itself. Hopefully you had some time to enjoy it. The folks I know who did the ERR seemed to. 

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I was to busy looking at the photos and missed it also. I'm surprised he's gone with off axis fibre and not just 0's for the web. I wonder if that is to help transfer torsional loads down the blade? I guess the blade itself is probably quite stiff side to side already just with it's carbon skins. 

Sub 10lbs.. probably weighs less then a laser rudder.

image.png.0a5b61f2a1723887018ba4127235924e.png

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It's a foam-cored shear web; it's not there as a stiffener, but to join the blades sides so they act like an "I-beam".

The UD stiffening laminate is all in the blade skins.

I was going to add a full covering laminate to the blade, but the bugger was so stiff I didn't; see any need for it.

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15 hours ago, Great Red Shark said:

Sure looks good - I haven't seen the 20 in a LONG time!  Still going to (re)use the M24 bulb or going custom?

Thanks for the updates

He shared the bulb build starting around here:

 

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  • 3 weeks later...
On 9/26/2021 at 10:11 PM, Varan said:

Bump...

Whatz zappening... Any progress?

Just back from a trip to West Coast to visit Moms and drive a car back to Vermont; took the northern route through Canada; vaccination/test requirements are very strict, and only saw 3 other US license plates after driving 3500 miles in Canada. Brought my table and chop saws back with me, and a roll of carbon. Looking forward to getting some shit accomplished now!

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  • 3 weeks later...

getting back to work . . .

Laminated boom halves in GP 26 mold; used the front and back molds to get a boom 3 meters long  x 160mm deep; the front half will be the bottom of the boom with a soft radius so easy on spinnaker sheets. Before trimming, gluing, adding end reinforcements, and an extra 200gsm (6oz) carbon covering laminate, we're at 7 lbs, 2 oz. Expect to be just under 10 pounds finished :D

Built the joining plates using the 34 footer's boom as a "mold". 

Extending the repaired Melges 24 mast 950mm to facilitate steeping the mast on the keel frame; it's better for the mast and a more seaworthy setup. 

Will get boom and mast extension progressed next week and work on keel fin mold/parts. 

Just need a tiller  . . .

Boom 1.jpg

Boom 2.jpg

Mast 1.jpg

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Forgot to mention the solar post curing for the boom parts works great. Last time I di d that was in Hawaii. Vermont is becoming the sun-belt with all the global warming going on.  Guess you need to be here to understand how that's working . . . 

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6 hours ago, Jim Donovan said:

Forgot to mention the solar post curing for the boom parts works great. Last time I di d that was in Hawaii. Vermont is becoming the sun-belt with all the global warming going on.  Guess you need to be here to understand how that's working . . . 

I do that all the time here in Utah at nearly 7000 feet of elevation. The sun is intense. I take the parts outside and put them on my front deck and it's an excellent oven.

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Getting cold up here in Vermont, and all the boats are heading for the shed.

Meanwhile . . . 

Getting near the finish line on the Melges 24 mast extension; the very small size of the section makes it difficult to fit tools/hands/anything inside it, so have to "invent" tools that fit. Spend a lot of my waking hours sorting out how to make this all work :wacko:.

The original mast section was typically beefy at the lower end, and I need to match the section properties to avoid a weak spot in the the tube. Fortunately this is well below the part of the mast that affects the mainsail luff curve.

I laminated tapers in the new extension parts and ground a taper in the old mast; this will allow me to add layers to the exterior of the mast. Without creating a "bump" in the section. (you can see this in the photos). Success happens when it all looks like it was always there.

My extra 950mm (37") extension piece doesn't have a tube molded into it, so I needed to make a smooth transition between the existing section and extension; using a die-grinder I was able to taper back the tube about 8" into the old mast. The material in that tube needed to be duplicated in the extension: a stack of 9 x 300gsm carbon unis was added to the lower section, tapering back into the original mast and extending down the length of the extension.

Prior to fitting the lower section, I made a similar carbon uni stack for the upper half; I made sure this would release from the tube so it would not be in the way as I fit the lower half (several hours laying awake one night sorted out how that would work).

Aligning everything perfectly was quite challenging; the laser level was essential.

Bottom half is now 100% attached to the mast, and I'm ready to fit the upper half parts.

After that, I know there's enough carbon to handle the loads, and the exterior patch is almost cosmetic. In reality, the exterior patch will be almost as good as the original laminate.  

 

 

Meges 24 Section.jpg

Mast Extension 1.jpg

Mast Extension 2.jpg

Mast Extension 3.jpg

Mast Extension 4.jpg

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  • 2 weeks later...

Added reinforcements to the boom at inboard & outboard ends, vang fitting, and mainsheet. Next time I'll add these with the shell laminates. With the shell in halves, super easy to add these inside the section and avoid complicated fairing on the exterior of the section.

Boom halves glued together today after installing vang fitting. Weight looking good at 8 lbs 6oz. 

Will add a 0/90 covering laminate to help stiffen the sidewalls and keep the join from opening up. Expect to be near 10 lbs when it's finished.

The little screws holding the join closed are the method I've found most useful for keeping the top/bottom aligned and clamping the interior joining plate. The screw holes are at the middle of the "beam" and don't compromise the structure much at all; that and they're through the sidewall plus backing plate, so in a doubled up area.

Stuck the heat gun in the section for about 4 hours to cure the glue; then pulled the screws before they became too attached (been there before :huh:).

 

 

Boom 3.jpg

Boom 4.jpg

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Boom is getting prepped for final covering laminate; 200gsm cloth @ 0/90.

This does two things; adds a 90 degree fiber for "hoop strength", and covers the join so it has little to no chance of splitting open.  The thing about glue joints is that they fail by opening at one end, and then peeling open along the full length; the "Achilles heel" of a glue joint. Some builders leave fasteners in the joint to prevent this peel failure; I prefer to leave 1 ply off the laminate, and then add it after the parts are joined. Its quite amazing how strong 100gsm (3 oz) of carbon fiber can be applied across a seam. Used the same method for the 120ft AC masts. 

I made a sanding board for the 34 footer's boom. Quite simple; 4 x layers of 1208 DBM ( 12 oz double bias + 1.5oz chopped strand mat) laminated onto a faired section of the boom. The 34 footer boom was built using two GP26 aft mast sections , so this sanding board worked for the top and bottom; the result was really nice :D.

I used a front and back of the GP 26 mold for this boom, so the same sanding board works for about 80% of the 20 footer's boom. I'll need to sand the front (boom bottom) by hand - sanding a big radius like this is quite simple if you  make sure you use a long board sanding on the diagonal.

 

Boom 5.jpg

Boom 6.jpg

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Mast prepped for laminate over the joint, and laminate applied.

"Heat gun" stuck in the end of the mast to help with curing the laminate. We're just starting to get freezing temps at night, and the shed temp is in the mid 50s; epoxy gets really thick and takes days/weeks to cure at these temps, so localized heating of the resin and laminate is absolutely necessary. As it turns out, hair dryers are just about perfect as a heat source for epoxy laminates. They don't get too hot, pump out a lot of air to circulate the heat, and are really cheap ($20). I have much nicer heat guns that I save for bigger parts.

I like to cure parts at around 160 degrees F; the ProSet resin I'm using will take half a day at this temp to get anywhere close to "hard".  

The difference in epoxies is quite interesting. Proset is the "professional grade" West System epoxy. It's MUCH better than the standard West 105 resin, but has the downside where it requires elevated temps to move beyond partial cure. it will stay gummy and unworkable for days at temps below 70 degrees. I use West 105 for faring parts; it cures rapidly at low temps and is much softer (easier to sand).

 

Mast Extension 5.jpg

Mast Extension 6.jpg

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I guess I need to emphasize that using heat guns/hair dryers requires 100% attention. You CANNOT just leave the shed with them running unless you want to set a fire. The nozzle temp on these heaters will set things on fire, and you need to be super careful, and constantly check that you're not f-ing up. 

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Great thread, Jim! 
Interesting that you have pre made sawhorses…I’m thinking that your too busy to knock a few out or someone gave them to you. Either way,  they are stable platforms and your work is impeccable.

 

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Did you vacuum bag on your 0/90 last layers or did you do a wet layup? I would assume the latter given the pic with the hair dryer but I wasn't sure if that was a post cure situation.

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A vacuum bag is used on many types of laminates; pre-preg and infusion can't done without a vacuum bag. Wet lam can be accomplished with or without a vacuum bag. When you're sticking many layers of wet-lam together, the bag helps enormously to consolidate the layers and extract air trapped between plys. On thin laminates, I can consolidate the laminate by hand, so will often not use a bag.

I applied the joining laminates in two stages, so I was only applying 4 plys at a time. It's much easier to consolidate and control resin content with fewer layers. 

And sometimes a bag will create wrinkles in a laminate; you see it all the time, especially on laminates that go around a corner (I'll look for some photos and post).

I've never thought those wrinkles were a good thing for a material like carbon, and a little extra resin and air would produce a better structure. Haven't tested that idea yet; might be a good idea to do exactly that. 

 

 

 

 

 

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16 hours ago, Jim Donovan said:

A vacuum bag is used on many types of laminates; pre-preg and infusion can't done without a vacuum bag. Wet lam can be accomplished with or without a vacuum bag. When you're sticking many layers of wet-lam together, the bag helps enormously to consolidate the layers and extract air trapped between plys. On thin laminates, I can consolidate the laminate by hand, so will often not use a bag.

I applied the joining laminates in two stages, so I was only applying 4 plys at a time. It's much easier to consolidate and control resin content with fewer layers. 

And sometimes a bag will create wrinkles in a laminate; you see it all the time, especially on laminates that go around a corner (I'll look for some photos and post).

I've never thought those wrinkles were a good thing for a material like carbon, and a little extra resin and air would produce a better structure. Haven't tested that idea yet; might be a good idea to do exactly that. 

 

 

 

 

 

That was why I asked, when I've bagged carbon on tubes, it doesn't always go so well. 

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  • 2 weeks later...

Lots of other stuff going on the past couple months, including a Trans-Canada drive (Vancouver BC to Ottawa), getting all the boats back in the shed, and generally prepping for another Vermont winter.

Remember the keel fin?

Along with adding the last covering laminate on the boom and faring the mast extension, I'm back working on the keel fin, finished the port mold half 

 

20 FIN MOLD 1.jpg

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Sealed the mold surface with a juicy layer of 6oz glass, and then used packaging tape for a release surface. The tape overlaps leave minor ridges in the parts; super easy to fair out as long as you plan to paint the part. I leave the leading edge off the fin so I can get a rock solid joining laminate at the leading edge; Added a 2mm stack of glass laminate to accept 4 x 400gsm carbon tapes. There will be a kelp cutter on the fin, and that's "easy" to do with a fin built this way.

20 FIN MOLD 4.jpg

20 FIN MOLD 5.jpg

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First stack of laminate in the mold yesterday. I need to heat the resin now because the shed's at about 55 degrees. The resin gets nice and viscous heated to 80 degrees, which makes the wet-out process go better. With the cool shed temps, no problem getting 6 layers in the mold without the mass of laminate heating up and starting to cure before the bag goes on (that's a typical Hawaii problem).  Have another 4 x full length layers, followed by 13 layers that taper in length; 23 layers total.  

20 FIN MOLD 6.jpg

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First half of the boom covering laminate on and trimmed yesterday; still developing techniques to get a "perfect" seam line between the two laminates. Wrapping a laminate around a part proves to be insanely difficult, so I've found doing this laminate in two halves more successful. The 90 degree fibers in this laminate are all about beefing up and stiffening the sidewalls, so they don't need to be continuous around the tube. 

Boom 7.jpg

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12 hours ago, Jim Donovan said:

BTW

Was in Annapolis a week ago to help a friend deal with a boat issue.

Cruised through Rod Jabin's yard and saw this - really Mike?  

GP 26 Hull 4 (had a different name when it was in San Diego :wacko:)

Rattle n Rum.jpg

Love the GP26 and that one in blue is gorgeous. 

Speaking of blue, great to see the Patriot Sailing Melges 24 in the background. Really nice guys, sailed against them at Charleston last April.

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Thank you, Jim for continuing to share details and photos as the build progresses. They're always interesting and I always learn something.

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Ran out of sealant tape after the first fin laminate, so shifted to other stuff, like making fresh pasta and baguettes.

And progressing on various tasks for the 20.

Put a couple coats of primer on the lower third of the mast to see what I had - really difficult to see fair shapes when there's surfaces that are black, white and beige. Initial impression is what I wanted; you can't see where I added the 1 meter long piece. 

Mast Primer.jpg

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The boom got it's final covering laminate, and after doing a similar procedure for the 34 footer's boom, I found a method that gets a very nice seam between the laminates. wrapping a laminate really tight around a tube and keeping the weave straight is super difficult. Since this covering laminate is primarily stiffening the sidewalls while adding 150gsm of carbon across the joint, it doesn't need to be continuous around the tube. Want to finish this tube w/clear coat. Weights right in target at just under 10 lbs.

Boom 8.jpg

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