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alanvdh · 02-08-2010, 07:07

Hello All, I'm still at the research stage (Short of funds still). I have toyed with the idea of buying a real beat up GRP sailboat, 36 - 40 ft, and slowly fixing it as and when the finances allow. I have however come across Dudley Dix website as a result of seeing one of his designs in Richards Bay South Africa and and became intrigued with his Didi 38 - 40 -40cr designs build from marine ply.
Can any of you tell me if this method of construction is as strong as GRP?
He certainly had no qualms sailing his on "Black Cat" across the Atlantic.
He is one of the most reputable designer / builders
The plan is a circumnavigation, so strength is a priority.
Cheers,
Alan

svHyLyte · 02-08-2010, 07:51

Molded plywood is as strog as, if not stronger, than glass reinforced plastic and certainly lighter for a given strength. The predominance of GRP in yachts arises from the fact that it is easy to construct with relatively unskilled labor and the materials are relativel inexpensive. It is also easier to repair when damaged, again with less skilled workman, and is not subject to potential deterioration if "abused" as is a cold molded ply hull. Frankly, I don't think a glass hull compares in any regard with a well made wooden boat; but, I wouldn't want the maintenance issues.

FWIW....

alanvdh · 05-08-2010, 06:22

Hello All,
I have just ordered the study pack for the Didi 40cr.http://www.dixdesign.com/didi40cr.htmFirst step done!
Cheers,
Alan

jpemb7 · 07-08-2010, 04:47

Plywood boats were a very popular boat construction material in Australia before fibreglass really took over.
I have a farrier trimaran built from plywood epoxy saturated (west System) with the exterior completely glassed. My boat was built in 1986 and it is as dry and sound as ever. It was beautifully built.
The problem is that most plywood boats are/ have been homemade so there were some pretty poor quality project boats out there which gave plywood a bad reputation. Construction technique using plywood is generally easier and less expensive than fibreglass or other synthetics. All boats have htere maintenance issues. The only issue mine has is that it has to be repainted every 5 years or so. But a well made plywood boat is as good as a well made fibrglass boat, steel boat or ferro cement boat. But with plywood like ferro cement and to a lessor extent steel you tend to take a hit when you try to resell, so you need to buy it at a good price.

Factor · 07-08-2010, 05:09

What he said - I had a modern epoxy ply tri (Kendrick avalon - see below)) and it was very strong. Easy to look after, only thing is - if you drill a hole do it oversize fill it with epoxy and then wait and then screw into it. If I was building a boat - then a modern epoxy ply would be certainly in the mix.

PAR · 07-08-2010, 08:53

Pound for pound, plywood is stronger then steel and easily stronger then GRP.

alanvdh · 07-08-2010, 12:06

Hi Guys, I'm really chuffed with the positive responses so far. I'm pretty handy when it comes to wood and l would have total confidence in the quality by building her myself as opposed to buying used.
Thanks,
Alan

maxingout · 07-08-2010, 12:27

When you purchase a used homebuilt plywood yacht, you don't really know what you are getting. The problem with many amateur built boats is that the home builders sometimes don't follow the construction methods and instructions made by the yacht designer. They cut corners or try to make things better in their own judgment. Sometimes they get it right, and sometimes they get it wrong. The problem is that you don't know where they have cut corners and made compromises that are not up to standard. It's impossible to inspect all of their construction in many places on the yacht.

When you build it yourself, and you do it right, you know what you are getting.

alanvdh · 07-08-2010, 12:48

Thanks All,
When it comes to building, repairing etc. I'm pretty thorough and I spend a lot of time researching and analyzing. This saves me a lot of time not having to do it twice.
Cheers,
Alan

MichaelC · 07-08-2010, 15:49

Building in ply makes good sense. Be sure you use multiple layers and glue the layers well. 3/8" ply is easy to work with and several layers make a strong, tight hull and deck. Look at Buehler's book [Backyard Boatbuilding] for ideas and instruction on building inexpensive, skookum boats.

PAR · 07-08-2010, 17:53

George Buehler's techniques, in regard to plywood should be taken with the same disdain he has for the material. He hates the stuff and will avoid it if he can. He has finally come aboard the encapsulation and sheathing methodology ship, but it was hard fought. George's building techniques only work on his designs (or similar), which are very burdensome craft, who's massive scantlings make them cost a lot more, then more modern building methods (a vessels displacement is directly related to build cost, and his boats are "fat" to say the least). Also, you don't need to "layer" the plywood. It's already layered, though using good quality, marine grade plywood always pays for itself in the long term and especially at resale.

I design a lot of boats for the back yard builder. The single biggest issue with a home built plywood boat is weight from over building. Most think they can add a little here and add a little there, all in an effort to make it stronger. Unfortunately, this is a common, first year engineering student mistake. Usually, this methodology makes the structure weaker, increases stress risers, point loading and of course makes things heaver which decreases load capacity, stability, etc. The best advise is build to the plan or call the designer and discuss the planned changes.

The second most common mistake of the home built boat is material substitution. Using home improvement store plywood instead of marine, using 304 stainless from the hardware store, thinking that drywall adhesives will work to hold a hull together, etc. These choices can leave you with a child only a mother could love and a short life span. If you find a great looking hull that has "Liquid Nails" holding the planks to the frames, run in the other direction as quickly as you can.

If contemplating this type of purchase, look for encapsulation, solid, intact sheathings, reasonable building practices, the quality/condition of the fasteners and hardware.For the most part, unless you can physically meet and talk to the actual builder, home builds will be a crap shoot. The level of finish is usually a good indication of the builders interest and skills. So, if they couldn't get the hull fair before they applied the paint, you have to ask yourself what else couldn't they do properly.

MichaelC · 10-08-2010, 17:37

If you are building for yourself, Buehler's techniques are neither burdensome nor expensive. My 32' DE cutter will go into the water for under ten thousand in materials. Expensive designers do NOT want to hear about boats like this. they want you to build boats with 2 heads, 6 bunks and a great cabin in under 40 feet - an idiotic approach. Do the research, and don't listen to just one guy. Another excellent boat designer for home builders is Tom Colvin. If you are to purchase a design, ALWAYS find out if the designer has crossed oceans and lived aboard in his own designs. That fact alone will tell you much.

**GordMay** · 10-08-2010, 17:57

Quote:

Originally Posted by MichaelC

... If you are to purchase a design, ALWAYS find out if the designer has crossed oceans and lived aboard in his own designs. That fact alone will tell you much.

A designer cannot have designed very many boats, if he will have crossed oceans and lived aboard each of them.