Cruisers Forum
 


Join CruisersForum Today

Reply
 
Thread Tools Rate Thread Display Modes
Old 02-08-2010, 07:07   #1
Registered User

Join Date: Jun 2010
Location: United Kingdom
Boat: Wauquiez Gladiateur 33
Posts: 50
The Strength of Marine Ply and Cold-Molded Ply

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
__________________

__________________
alanvdh is offline   Reply With Quote
Old 02-08-2010, 07:51   #2
Registered User
 
svHyLyte's Avatar

Join Date: Mar 2006
Location: Tampa Bay area, USA
Boat: Beneteau First 42
Posts: 3,432
Images: 25
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....
__________________

__________________
"It is not so much for its beauty that the Sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."
svHyLyte is offline   Reply With Quote
Old 05-08-2010, 06:22   #3
Registered User

Join Date: Jun 2010
Location: United Kingdom
Boat: Wauquiez Gladiateur 33
Posts: 50
Hello All,
I have just ordered the study pack for the Didi 40cr.http://www.dixdesign.com/didi40cr.htmFirst step done!
Cheers,
Alan
__________________
alanvdh is offline   Reply With Quote
Old 07-08-2010, 04:47   #4
Registered User
 
jpemb7's Avatar

Join Date: Jan 2010
Location: Mooloolaba, Australia
Boat: Farrier Command 10 Tri
Posts: 183
As good as the builder

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.
__________________
jpemb7 is offline   Reply With Quote
Old 07-08-2010, 05:09   #5
Marine Service Provider
 
Factor's Avatar

Join Date: Dec 2006
Location: Brisbane Australia
Boat: Corsair Dash MKII
Posts: 4,084
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.
Attached Thumbnails
Click image for larger version

Name:	Sags 10th Aug 08 005.jpg
Views:	354
Size:	418.2 KB
ID:	18252  
__________________
Factor is offline   Reply With Quote
Old 07-08-2010, 08:53   #6
PAR
Registered User
 
PAR's Avatar

Join Date: Jul 2010
Location: Eustis, FL
Boat: 1960 Chris Craft, 1957 Clyde, 1961 Atkins, 1986 Macgregor 65, plus three of my own design and build
Posts: 239
Images: 2
Send a message via Skype™ to PAR
Pound for pound, plywood is stronger then steel and easily stronger then GRP.
__________________
PAR is offline   Reply With Quote
Old 07-08-2010, 12:06   #7
Registered User

Join Date: Jun 2010
Location: United Kingdom
Boat: Wauquiez Gladiateur 33
Posts: 50
Thumbs up

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
__________________
alanvdh is offline   Reply With Quote
Old 07-08-2010, 12:27   #8
Senior Cruiser
 
maxingout's Avatar

Cruisers Forum Supporter

Join Date: Dec 2006
Location: Fort Pierce, Phoenix
Boat: Privilege 39 Catamaran, Exit Only
Posts: 2,606
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.
__________________
Dave -Sailing Vessel Exit Only

http://SailingUNI.com
http://maxingout.com
http://PositiveThinkingSailor.com
maxingout is offline   Reply With Quote
Old 07-08-2010, 12:48   #9
Registered User

Join Date: Jun 2010
Location: United Kingdom
Boat: Wauquiez Gladiateur 33
Posts: 50
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
__________________
alanvdh is offline   Reply With Quote
Old 07-08-2010, 15:49   #10
Registered User

Join Date: Nov 2009
Location: Bellingham WA
Boat: 17' faering Ironblood, building 34' schooner Javelin
Posts: 305
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.
__________________
MichaelC is offline   Reply With Quote
Old 07-08-2010, 17:53   #11
PAR
Registered User
 
PAR's Avatar

Join Date: Jul 2010
Location: Eustis, FL
Boat: 1960 Chris Craft, 1957 Clyde, 1961 Atkins, 1986 Macgregor 65, plus three of my own design and build
Posts: 239
Images: 2
Send a message via Skype™ to PAR
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.
__________________
PAR is offline   Reply With Quote
Old 10-08-2010, 17:37   #12
Registered User

Join Date: Nov 2009
Location: Bellingham WA
Boat: 17' faering Ironblood, building 34' schooner Javelin
Posts: 305
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.
__________________
MichaelC is offline   Reply With Quote
Old 10-08-2010, 17:57   #13
Moderator Emeritus
 
GordMay's Avatar

Join Date: Mar 2003
Location: Thunder Bay, Ontario - 48-29N x 89-20W
Boat: (Cruiser Living On Dirt)
Posts: 31,579
Images: 240
Quote:
Originally Posted by MichaelC View Post
... 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.
__________________
Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"



GordMay is offline   Reply With Quote
Old 10-08-2010, 18:03   #14
cat herder, extreme blacksheep
 
zeehag's Avatar

Cruisers Forum Supporter

Join Date: Jul 2008
Location: furycame alley , tropics, mexico for now
Boat: 1976 FORMOSA yankee clipper 41
Posts: 17,770
Images: 56
Send a message via Yahoo to zeehag Send a message via Skype™ to zeehag
Quote:
Originally Posted by GordMay View Post
A designer cannot have designed very many boats, if he will have crossed oceans and lived aboard each of them.
truer words i havent heard spoken...
zeehag is online now   Reply With Quote
Old 10-08-2010, 19:08   #15
Moderator
 
Boracay's Avatar

Cruisers Forum Supporter

Join Date: Feb 2004
Location: Pelican Bay, Great Sandy National Park
Boat: Steel Roberts Offshore 44
Posts: 5,175
Images: 18
Two hulls?

Most ply monos have a very poor resale value.

Have you considered a catamaran? Size for size they could cost less than a mono when amateur built.
__________________

__________________
Rust never sleeps
Boracay Blog.
Boracay is offline   Reply With Quote
Reply

Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Cold-Molded Boats Cowboy Sailer Construction, Maintenance & Refit 42 22-05-2015 15:49
Problem with PLY and REF Points when Georeferencing BSB Charts draagedo OpenCPN 21 24-02-2010 06:57
Marine ply VS Pressure treated ply easterly Construction, Maintenance & Refit 12 09-09-2008 12:26
cold molded catamarans indypopeye Multihull Sailboats 0 29-01-2008 10:17
Cutting veneer ply - any tips? Weyalan Construction, Maintenance & Refit 11 02-10-2006 01:46



Copyright 2002- Social Knowledge, LLC All Rights Reserved.

All times are GMT -7. The time now is 14:39.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.