Reduce weight of nested dingy

anonymous · Post by **anonymous** » Fri Oct 18, 2002 11:54 pm

What are the risks if any of building the nested dingy with 4 mm Okume.? Would it work if I fiber glass exterior hull? I´d like to reduce weight. <IMG SRC="images/forum/icons/icon_smile.gif"> Ira Okun E mail <a href="mailto:iraokun@earthlink.net" target="_new">iraokun@earthlink.net</a>

anonymous · Post by **anonymous** » Mon Oct 21, 2002 10:50 am

Anon, If you cover 4mm wood with glass and resin, you very quickly lose any weight and cost advantage over bare 6mm wood. Glass sinks, so it´s denser than wood. Properly mixed S3 is the same density as water, so it´s also denser than wood. So you´re going to be replacing 2 mm of lightweight wood with probably the same thickness (at least) of heavier stuff. Also, I haven´t seen any of the 4mm okoume, but the 6mm stuff I use is 5-ply. My guess is that the 4mm just omits a ply for the reduced thickness (anybody out there confirm this?). If this is the case, then you´d also be losing a layer of unidirectionally grained material and replacing it with material that has the grain running in 2 directions (woven cloth). Since half those fibers won´t be doing you any good structurally, you´d actually end up with a heavier and weaker boat if you used thinner wood and glassed it than if you used thicker wood and left it unglassed. The bigger boats from bateu.com use bidirectional (not woven) cloth with a carefully designed lamination schedule to take advantage of the fiber orientations. This is a carefully engineered composite structure which is pretty different from just glassing over some thinner wood. That´s why they can get away with using glass cloth for structural purposes. As far as just thinner wood with no glass, that´s a question for Evan (the fb11 designer) to answer. Good luck, Laszlo

anonymous · Post by **anonymous** » Mon Oct 21, 2002 10:54 am

Correction to above - I meant to say biaxial, not bidirectional glass. Laszlo

Post by **jacquesmm** » Mon Oct 21, 2002 12:48 pm

I did not respond because we are currently working on something related to that question. Last Thursday, I did spend the day with Jeff at WorldPanel and we agreed on selling plywood to our builders at a discounted price. Later today or tomorrow, you will see plywood links appear at our sites. What does that have to do with a lighter FB11? A lot. Because we know the exact specifications and quality of the plywood we will use, we can reduce our safety margin in hull materials. The FB11 can be built from plain fir or from quality marine ply but if you use our BS1088 Meranti marine, you don´t need it to be 6 mm (1/4"). Thinner plywood will work. The Meranti 4 mm that I saw at WorldPanel would be perfect for the job. At 4 mm, it will be stronger than cheap fir in 6 mm. Fiberglass lamination will stay the same. Now, this applies to that specific plywood. It is not valid for any 4 mm plywood. Ours is not only BS1088 but also rated at the top by Lloyds.

JimW · Post by **JimW** » Wed Oct 23, 2002 12:41 pm

Jacques, That is great! I always thought that you partnering with a place like world panel would be an ideal fit if the details worked out. I think you and Jeff will both gain from it. One of the "foggiest" issues for new builders is sources for good plywood. Jim

Post by **jacquesmm** » Wed Oct 23, 2002 12:53 pm

Glad to see that builders approve. I know Jeff and WorldPanel since years: they shipped plywood for us to remote places like Panama. The quality of their products is very high and Jeff understands our requirements. His office manager knows boats: Leif will build an OB19 soon. That means that those guys understand exactly what our builders need. An agreement between our companies was bound to happen, we were simply procrastinating. Another good side of this deal is that Jeff and Leif will monitor the plywood message board several times a day. They will respond to questions and I will ask them to review our plywood FAQ. I should be ready with the first web pages about plywood before the end of the week.

fishingdan · Post by **fishingdan** » Wed Oct 23, 2002 2:14 pm

For what it is worth, I think this is a great idea. In some areas of the country it is not easy to find the required plywood. As you know, it is very expensive to have the wood shipped (particularly a small order shipped to a home = an extra charge in many cases). At least we will be able to purchase from a trusted source that is familiar with our activities. Any group discounts that could also be passed on would be a big plus!

Post by **jacquesmm** » Wed Oct 23, 2002 3:56 pm

Yes, discounts will apply and shipping costs will be a very good surprise. I have read on this board about some of builders paying more to ship 80 miles than what we will charge to ship across the country! <IMG SRC="images/forum/icons/icon_wink.gif">

anonymous · Post by **anonymous** » Thu Oct 24, 2002 12:33 am

Hi, I would be a bit reluctant to approve the use of 4mm ply for the nesting dinghy if you were planning to use it with the sailing rig. It might be a bit too twisty when hard on the wind and really heeled over. Thicker plywood provides more stiffness. Glassing 4mm will bring it up to the weight of 6mm ply very fast and won´t save you weight. Otherwise it would be o.k. BUT only with a very high quality plywood as Jacques has described in his posting. Lesser quality ply just won´t have the strength required. However, after using the boat for several years as a yacht tender, I can tell you that the total weight isn´t that much. Two people can easily carry it up a beach with a smile on their faces without straining, and if it´s just you alone, it´s light enough to drag up the same beach. If you regularly abuse your boat like I do (dragging it up rocky beaches etc) then you would agree that the 6mm gives you that extra resistance to punctures. Evan Gatehouse (the FB11 designer)

Post by **jacquesmm** » Thu Oct 24, 2002 8:53 am

The designer should have the last word not only because he is the designer but also because he used the boat and knows its limits. No 4mm if you build the sailing version.

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