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Require Tips on Fibre Sheathing

Postby waynet on Sun Apr 19, 2015 10:49 am

Hi to you all,

I am about to start a build on my first Sabre. I am using 4mm Gaboon all round and would like to know where on the hull I need to put fibre sheathing to strengthen and stiffen the hull. Do I need to put sheathing on both sides of the hull before stitching/joining etc? I am not too concerned about a little extra weight, only want the boat to be sturdy and durable because of the 4mm ply.

Thanks in advance.

Waynet
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Re: Require Tips on Fibre Sheathing

Postby Aten on Mon Apr 20, 2015 7:51 pm

Hi Wayne,

There is discussion on this on the forum somewhere. From memory the ply can be glassed on the inside prior to stitching but gets very hard to bend the bow to the right shape if you glass too far forward. From what I know the outside gets glassed later. If you trawl the forum threads you should find most of what you need to know.
There are plenty of guys out there who have built these fine sailing machines. I'm sure someone can post here with acurate info.
Craig
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Re: Require Tips on Fibre Sheathing

Postby Aten on Mon Apr 20, 2015 7:54 pm

Have you cut your panels yet? Where are you located?

Craig
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Re: Require Tips on Fibre Sheathing

Postby waynet on Mon Apr 20, 2015 8:24 pm

Thanks Craig, no I haven't cut the panels yet. I am trying to collect enough information together before I start and sheathing was one question. It makes sense not to sheath the twisty bits first. I want the floor to be strong so do I sheath the inside of the floor panels first before assembly and then sheath all of the outer hull later?
waynet
 
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Re: Require Tips on Fibre Sheathing

Postby Aten on Tue Apr 21, 2015 4:24 pm

I have only built a FRP Sabre so I am far from being an expert on ply boats. One thing that I have learned is that many of the ply hulls develop cracks on the floor right next to the stiffening ribs. This seems to be caused by the odd heaving landing after a bad tack or near capsize. What I am getting at here is to at least glass the inside of the hull between the centre case to roughly one metre back from cenre case.
Give me a call if you get a chance. I have a bit of info that is not common knowledge yet that will likely help you with your ply boat construction.
Craig 0417172453.
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Re: Require Tips on Fibre Sheathing

Postby harold on Tue Apr 21, 2015 11:49 pm

Hi Wayne
I built my own ply Sabre and got advice from a professional. Glass the inside of the floor panels when they are flat from the transom to just about 50mm past the Centrecase bulkhead. Go further and you will find the panel too stiff to bend. You can stop just inside the side tank too. The forward part of the hull is inherently stiff from its shape so you don't need glass there. I used a cheap plastic spreader roughly 100mm wide, the sort of thing you get from Bunnings for a dollar. The resin chips off when set so you can use it time and time again. Make sure you use as little resin as you can leaving a clear texture from the glass to keep the weight down.
When you have your hull largely complete with bulkheads and side tanks in place you can coat the outside. Again go for a slight texture and use a high build undercoat to smooth the finish. You do not need to go past the centre case bulkhead for strength but you might improve the impact resistance in case of a crash.
One other word of advice if you haven't started or have not got very far. Build yourself a 'strong back'. Thats not to keep you fit but to make sure the rocker measures. A 'strong back' is a very stiff beam along the centre line of the hull which is cut precisely to the rocker profile you want to produce. Build your boat on top of that and make sure the rocker does not pull away from it. Its good to have a supporting frame attached to that to stabilise the boat as you build. Ply boats do tend to have a bit of a mind of their own and move as you build them so keep checking that and all the other measurements.
Another word of advice. Check out the west system brochure on filleting the joints. Makes a very much stronger joint of the stitch and glue. Email me on medd@tpg.com.au if you need more help.

Enjoy the building and then the sailing
Harold
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Re: Require Tips on Fibre Sheathing

Postby waynet on Wed Apr 22, 2015 4:35 am

Hi Harold,
Brilliant article, much appreciated :D

Cheers,
Wayne
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Re: Require Tips on Fibre Sheathing

Postby Aten on Wed Apr 22, 2015 12:13 pm

Some links here for pics of sabre building
http://www.boatinghardware.com.au/custo ... bre-build/
http://www.seabreeze.com.au/forums/Sail ... re-Dinghy/

From the Sabre forum- viewtopic.php?f=1&t=1975#p4202

FYI. I use short paint rollers for wetting/spreading fibreglass. Harold uses the squeegee method. Either way keep the resin to a minimum but be careful not to go too light as the ply can soak up a little causing the fibreglass to go dry and weak. Do not try to glass when it is too cold as the resin is hard to work with. 22 -25 degrees seems to be ideal. Hotter works too but reduces working time.
West systems resin is good but not the only type you can use. Well worth reading the info they publish. Most is available online. Their filler and glue powders are expensive. I use Q-cells for filler and fumed silica (Cabosil) for glue and a mixture of both for filleting. This stuff is cheap and easy to get.

Here is a good tip well worth knowing. A small amount of Cabosil mixed with Q-cell/epoxy filler make it spread much nicer.

Craig
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Re: Require Tips on Fibre Sheathing

Postby JohnL on Mon Apr 27, 2015 6:26 pm

Hi Waynet,

Welcome to the Sabre family.

I endorse Harold's comments about a strong back. I would further add that if you use a strong-back you make the spacer at the thwart the length that matches the finished hull because if you use the longer length recommended in the construction notes you will change the rock as you pull the sides in to get the beam correct.

I am about to start my 4th boat and will be using an aluminium batten to get the curve in the strong back and the bottom of the side panels fair. A fair boat will be faster than one with ripples from an unfair chine or keel line.

Put some of the yellow packaging tape on the top of your strong-back so if any resin goes through the joint the boat will not be stuck to the strong-back.

Regarding the glass I have used a short hair roller and a foam roller with little difference in the result. I live on the QLD Sunshine Coast so have little trouble with resin temperature.

The class rules and measurement notes call for panels 1 and 1A to be 5mm thick ply or 4.5mm thick glass / ply composite. My test and the literature published outside this forum indicates that this needs a layer of 200gms either side of the ply to comply. Please feel free to conduct your own tests.

I find that using the roller and working from the wet to the dry areas that my resin to cloth ration is around 1 resin to 1 cloth by weight and I end up with the finished laminate being between 0.1 to 0.11mm per 100gns of cloth. I have achieved these results with 100gms, 200gms, 300gms unidirectional cloth and 900gms unidirectional cloth. From a weight perspective This equates to about 200gms for every 100gms of cloth used. My experience is that 200gms cloth plus resin adds 4kg. if you go for 100gms then you will reduce that to 2kg.
If you reduce the area of glass you could save additional weight. Other posts on this forum suggest that aroung 100gms glass is all that is required. I think the heavier glass will reduce the cracking at the edges of the floor battens.

if you use a balance weave cloth run the fibres at 45 degrees to the centreline of the boat as this will end up with a stiffer panels and boat than the 0/90 direction.

I use the WEST resin because I like the ability to use metered pumps and I know all my glass and glue will be compatible.

If you ask Mr Google the right questions you will find lots of sites that have video's of how to do fibre glassing.

Have fun and enjoy the project. Read the construction notes several times before you start and read each step again before you do it and a couple of steps further ahead also. Take lots of care to keep everything clean and remove any excess glue and resin.

I am not sure about the floor batten length conditions now. I believe we can extend them further than 25mm through the Centrecase bulkhead. I am planning on making the floor battens around 3000mm long starting at the transom. This should strengthening the area forward of the Centrecase bulkhead considerably. I believe this area is critical in getting on to the plane early.

Regards JohnL.
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