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Layup schedule for Chameleon dinghy


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I have the plans for a Chameleon dinghy and am thinking of building it this winter.  This is a stitch and glue design.  I will be using 6mm plywood for the core.

The plans call for one layer of fiberglass cloth over the exterior of the hull, plus a layer of 4" tape and a layer of 6" tape on both the inside and outside of every seam.  The weight of the fiberglass isn't specified in the plans.  I would assume ~8oz woven cloth since this is a widely used weight for boat construction and repair and was also in widespread use when the design was made.  The plans suggest an optional layer of fiberglass cloth on the interior floor for abrasion resistance.

I would like to update the layup schedule to use higher performance materials, with the goal of improving durability, simplifying the layup, and perhaps reducing the hull weight slightly. 

Here's what I'm thinking:

  • Use 5 oz Kevlar fabric in place of the 8oz fiberglass for the exterior of the hull, for improved abrasion and puncture resistance.
  • Also use the 5 oz Kevlar fabric in the interior floor.
  • Use a single layer of 17 oz biaxial fabric, 6" wide, in place of the combination of single-weave 4" tape and 6" tape, for easier layup and improved strength.  (I'm avoiding kevlar here because compression strength is important)
  • Use 4 oz fiberglass cloth in less critical internal areas such as the inside of the daggerboard box and the faces of the mating bulkheads, to reduce weight.

I am also thinking of lightly coating the plywood with epoxy, allowing a full cure, and sanding after the panels are cut out and before stitching and gluing, for a more even and predictable wetout, and to have an epoxy coat as primer on the interior areas that aren't glassed.

Planning on having peel ply, clamps, and plywood scraps on hand to use on areas with overlap to get a fair surface from the initial layup with minimal need for filler.

Any advice?

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Kevlar is difficult to get a good finish on. Using peel ply is good, using a layer of light scrim or model cloth is better.

Kevlar thread doesn't cut when you sand it. It just gets fuzzy and won't take a finish. So you put something over it and try not to sand thru that.

Doug K

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46 minutes ago, Steam Flyer said:

Kevlar is difficult to get a good finish on. Using peel ply is good, using a layer of light scrim or model cloth is better.

Kevlar thread doesn't cut when you sand it. It just gets fuzzy and won't take a finish. So you put something over it and try not to sand thru that.

Doug K

Thanks, Doug.  I've worked with Kevlar before and know that cutting and sanding are, well, problematic.

I don't think I know what "model cloth" or "light scrim" is in the context of composite work.

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If building from 6mm ply 8oz is an overkill.  6mm ply is plenty strong and the glass is mainly there to hold the grain of the ply together to prevent water ingress as it ages. This does not take a lot, 6oz would be more than enough except for known abrasion areas.  I have built a lot of boats from ply and if it  was my dinghy I'd probably only use 4 oz as I would want it as light as practical. Instead of coating and curing and having to contend with the amine blush I would make sure the panels are cooling before applying a layer of epoxy. ( I have heated ply in the past to ensure this.) I would do the laminate  before the epoxy cures. It can be done all in one or after the epoxy goes tacky. Just harder to get the cloth in place without wrinkles if you wait until it is tacky.

As far as taping, Two layers of a diff width , narrower on top, would be easier to fair in than one heavier layer.

This is especially true if using peel ply as it will help so much with the lighter layers as it helps hold resin at same height and taper it  just off the edge of the tapes.

Tapering the edges  of the tapes with a tungsten scraper after cure is very quick and easy and would have it very close to  being done. So I'd use two layers of the  lighter cloth but in   double bias and probably only 4inches and 3 inches wide. None of the joints in my tri have tape any wider then 4 inches. If 4 inches won't do it you aint doin' it right.

I think Kevlar is also an overkill and makes building more difficult than it need be unless you plan on vacuuming. At least that could help with the Kevlar wet out.

BTW:- my friends 29ft cruising cat is only 6mm ply with 6 oz plain weave glass over the hulls and it has been doing great the last 16 years.

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4 hours ago, 2airishuman said:

Thanks, Doug.  I've worked with Kevlar before and know that cutting and sanding are, well, problematic.

I don't think I know what "model cloth" or "light scrim" is in the context of composite work.

2oz or 4oz surf cloth. Very fine. Easy to fill in the weave with a second coat of resin.  You can find it in regular weave and twill.

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18 hours ago, 2airishuman said:

The plans call for one layer of fiberglass cloth over the exterior of the hull, plus a layer of 4" tape and a layer of 6" tape on both the inside and outside of every seam.  The weight of the fiberglass isn't specified in the plans.  I would assume ~8oz woven cloth since this is a widely used weight for boat construction and repair and was also in widespread use when the design was made.  The plans suggest an optional layer of fiberglass cloth on the interior floor for abrasion resistance.

Here's what I'm thinking:

  • Use 5 oz Kevlar fabric in place of the 8oz fiberglass for the exterior of the hull, for improved abrasion and puncture resistance.
  • Also use the 5 oz Kevlar fabric in the interior floor.
  • Use a single layer of 17 oz biaxial fabric, 6" wide, in place of the combination of single-weave 4" tape and 6" tape, for easier layup and improved strength.  (I'm avoiding kevlar here because compression strength is important)
  • Use 4 oz fiberglass cloth in less critical internal areas such as the inside of the daggerboard box and the faces of the mating bulkheads, to reduce weight.

I am also thinking of lightly coating the plywood with epoxy, allowing a full cure, and sanding after the panels are cut out and before stitching and gluing, for a more even and predictable wetout, and to have an epoxy coat as primer on the interior areas that aren't glassed.

I designed a nesting dinghy, of which (many?) dozens have been built. It's very similar to Danny's design. It uses 6mm ply and a single layer of 9 oz tape inside and out at seams only. Covering the exterior is optional, and is only required if you use fir plywood which has a tendency to check. Our personal nesting dinghy with this construction lasted 4 years of full time cruising, 3 more years as a full time "row to work" dinghy, year round, before we passed it on to another cruiser when we sold our boat. It was plenty strong and durable.

I would consider changing the seams to a single layer of tape per my design. I think Danny's laminate schedule is very conservative and might represent a big safety factor to account for people who have no clue how to laminate.

I would only use 4-6 oz cloth on the exterior if you use fir plywood. I'd use meranti or okuome for better resistance to checking. The exterior cloth will help prevent bruises and dents in the wood, but I tend to consider my dinghy a workboat and didn't worry too much about scrapes etc.

I would not glass the inside. Paint will be fine to protect the hull once the hull is coated in epoxy.

I think pre-coating just adds work because you have to sand before glassing the seams. As a compromise maybe pre-coat but leave the 2" wide strip at the taped chines uncoated.

Most of the wear on our boat appeared on the keel from dragging it up sandy beaches. A single extra layer of tape on centerline is a good idea here. The mating bulkhead faces were only epoxy coated and painted and never saw any abrasion.

I would actually use thicker cloth inside the daggerboard box - it does suffer from wear and tear and you can't easily get back inside to repair it later.

I would not use a single layer of 17 oz - that's super thick and heavy. 

I have also designed the GV10, a 6mm ply planing boat. It has seams taped with 4" wide x 12 oz biaxial and the bottom inside and out is covered with 12 oz biaxial for the extra forces of a planing hull (25 knots or so). Sides are not fiberglassed. We had one for 4 years before it was stolen in Australia.

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@Zonker, thanks for the advice.  I was sort of hoping you'd post.  I like your FB11 design, hope you're able to retire on the royalty checks.

https://bateau.com/studyplans/FB11_study.php?prod=FB11.  - for any lurkers watching the thread.

I like the GV10 and GV11 also.  Right now I'm mainly interested in something to be rowed and sailed.  The layup for these planing boats is a good data point to contemplate though.

I will take your advice to switch to a single layer of (lighter weight) tape.  I will be using okuome.  I'm thinning out the buoyancy compartment sides to 4mm to save a pound or two.  I will also take your advice and refrain from glassing the inside.

Still contemplating the outside.  I will inevitably take it on river trips where I really shouldn't, you know, the ones with rocks and sand and branches and shallow spots.

I'm thinking of putting a piece of UHMWPE on the skegs.  https://www.amazon.com/dp/B000ILJZDY

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You can use West Marine G-flex to glue the UHMWPE. It actually works if you quickly flame treat the surface. Otherwise recessed screws into the skeg(s)

If  you're going to do river trips I'd think a light layer on the bottom only.

It would be awesome if I could retire on royalty checks but ... they are helpful for my daughter's university fund.

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I designed a little mini skiff for ply construction and the clients wanted to keep it very light yet be resistant to impact and abrasion. I wanted to use this fairly new composite called INNEGRA which may just be the old Vectra cloth with a new twist. I do know that the Army has helped a manufacturer to start production at an old textile mill in Enterprise AL which is right next door to the Army Air Corps Ft Rucker based helicopter Skunk Works. I looks like INNEGRA is poised to replace KEVLAR  for ballistics use in helicopter blades and body armor. Whitewater canoe and kayak people love it because it is so much easier to work with than KEVLAR and doesn't absorb water if the coatings get scratched or wear thin. 

 

 

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3 hours ago, Zonker said:

You can use West Marine G-flex to glue the UHMWPE. It actually works if you quickly flame treat the surface. Otherwise recessed screws into the skeg(s)

If  you're going to do river trips I'd think a light layer on the bottom only.

It would be awesome if I could retire on royalty checks but ... they are helpful for my daughter's university fund.

Thanks for that.  I've used G/flex for repairs on HDPE (flame treat and all) but it hadn't occurred to me that it would stick to UHMW. 

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7 hours ago, Zonker said:

You can use West Marine G-flex to glue the UHMWPE. It actually works if you quickly flame treat the surface. Otherwise recessed screws into the skeg(s)

If  you're going to do river trips I'd think a light layer on the bottom only.

It would be awesome if I could retire on royalty checks but ... they are helpful for my daughter's university fund.

Can you imagine how it feels to be WEST System epoxy, who were around decades before West Marine and have people constantly refer to you as West Marine? Not only are they different companies, they are completely different businesses and business models.

I know it was an honest mistake Zonker, but DON'T DO IT AGAIN!!!!

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10 hours ago, Zonker said:

Oops sorry.

You know I'm a huge fan of yours Zonker, I was just giving you shit.  It galls the hell out of WEST SYSTEM to always be referred to as West Marine. They keep their mouths shut about it as I should, but I just can't seem to be like them. I have a big mouth and can't seem to help it.

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