Recomendations for new transom material?

[85 starcraft]

Today we removed the old transom from our 21 ft. 1985 starcraft aluminum- hulled boat. The wood was starting to rot. When we extracted the transom we found that it was of 1 5/8" plywood ( marine?), 12 inches high by about 70 inches long.

Having done all this work, and having much to do to reinstall new transom material, I pose the following question to the gurus here: What is the absolute best transom material to use as a replacement? Marine Plywood vs. monolithic lumber vs. some kind of composite vs. foam core? And why?

Thanks for your help!

Carl

[PAR]

Oh Lord, here we go . . .

[85 starcraft]

PAR: Yes I'm new, and I'm not a professional boat-builder, but before posting the above question I did spend several hours searching this site's forums in an attempt to find an answer, or at least a consensus of opinion. Having read the transom-material debates in various forums re foam core materials vs. marine plywood vs. poor old Seacast [ pun intended], I concluded that marine plywood is clearly favored by at least a plurality of the pros here as being 'tried and true' and having known qualities, despite it's Achilles heel [susceptibility to rot]. Even so, there appear to be a number of boat builders who do seem to use composites and core material in "smaller boat" transoms with very good results.

In light of the above, and given that my boat is an all-aluminum hull and only 21 feet in length, I thought it reasonable to narrow my search by posting the above question on this sub-forum-- "metal boat building"-- in hopes of eliciting opinions from folks watching this particular subforum with experience, opinions and a willingness to provide advice to someone who is [re]building a metal boat. Can you see my thought process here?

I certainly did not mean to cause the 'inner circle' of Senior Members to roll it's collective eyes with an "Oh, no. Here we go again!" reply to my question.
If the question is stupid because it's been answered or debated before ad nauseum, is it too much trouble to at least point a newbie in the right direction? If there is no good answer to the question, how hard would it be to just say so?

Sometimes it's easy to forget that we all have to learn everything we know. Beginning from scratch.

Respectfully,

Carl

[marshmat]

I think at least part of the reason for PAR's frustration was that there is no right answer to your question. In the end, no known material will do what you want (strong, cheap and durable); rather, it's a matter of trading off cost versus longevity... and since there's no right or wrong answer, and certainly no 'absolute best', you'll be hard pressed to get a straight answer out of anyone. Unless they're trying to sell their own product of course.

I look at your problem this way. The original wood, probably without much protection (not like we have today at least), lasted 22 years. Modern plywood, with modern sealants, should last at least as long. By then you'll have either sold the boat or passed it on to the kids. Why change what works already?

[PAR]

I meant no offence, just that as Matt has suggested, it is a difficult question to offer definitive answers to.

In spite of draw backs, it's very difficult to match plywood's physical properties. This is why it's used so much in this structural element. Pound for pound, effort for effort and dollar for dollar, it's good stuff and most materials/methods will be hard pressed to compare at a similar level.

There are a number of engineering possibilities, most of which can be justified in some fashion, but the comfort level in working the method, price, and availability, make plywood had to dismiss.

An inert material would make life easy to deal with, when faced with a new transom, but then life takes a hard left and you're looking at the cost of a fancy core process, fairing exotic fabrics, etc.

In the end, you have to pick your own poison, depending on the particular qualifiers you've placed on it.

[85 starcraft]

Thanks, I'm going with plywood. Problem there is shipping costs; all the good stuff [e.g. Okoume BS1088] seems to come from the West coast and i'm in Atlanta.

[bilgeboy]

Yup.

The search function could also broaden your horizons.

Search all posts by Par, and you could write a book on boat repair.



This message paid for by Seacast TM.......:)

Mike

[85 starcraft]

Thanks Mike.

Believe me, I Have been using the search functions. For hours. And have found a wealth of info. And I have read enough of PAR's post to appreciate his status as a boat-building guru. My "newbie mistake' was thinking that I was pitching my transom material question solely to those into metal boat building/rebuilding on the metal boat building forum, which I presumed would be a much smaller group with a narrower focus; I was hoping there was a firmly held consensus there. I would not have intentionally posted such an open ended question for "general broadcast". My bad.

That said [and back on topic], I have decided to err on the side of being conservative and going with plywood [I'm thinking Okoume BS1088 at this point] and am searching for local suppliers in North GA/ Atlanta. I have located Southern Crown Boatworks at http://www.southerncrownboatworks.com/, but they specialize in wooden boat projects. Am still hoping to tie up with someone who does/knows aluminum hulled boats and is willing to give me some tips or advice.

Thanks for the reply.

Carl

[PAR]

Try www.woodfinder.com . . .

[tja]

Check with a good local marina to see if they have XL Panels made by Green Wood products. They make 3/4in. x 4ft x 8ft plywood that is preasure treated then kiln dried to 13 persent moisture. This product is used by many major boat manufacturers and is guarrented for life not to delaminate or rot for life or they will replace the wood along with any labor costs involved. One sheet will cost about $85.00 They have never had to replace any product to date. Good luck. Tom.

[August Ice]

Hello Im new to this site. I recently bought a used 16' Mirrocraft boat with a 75 hp suzuki motor... We took it out and after a few times out the transom began pulling away. We were filling with water.

Ive just removed all the rotten wood from the transom and the floor of the bow and under the dash. Ive been reading this article that seems similar but my transom needs to support a 75 hp motor. I ordered Okoume 1080 marine plywood but now Im reading up on how flexible this kind is and used for the hull and bow.... Is this the right kind of plywood for the support I need or should I get Maranti 1080? Or can anyone think of something that would be more supportive? I plan on wrapping it in fiberglass and have an aluminum sheet behind it for support (at least in part) The transom wood should
be 2' X 6'. Id greatly appreciate any help from you experienced boat builders.

Janet

[August Ice]

I found a plywood supplier with reasonable prices in No. Yarmouth, ME "Fat Andy's" Im not sure if this would be helpfull.

Jan

[alan white]

Hi Janet,

Okoume is fine. The most important thing is to seal it well with epoxy (you can get epoxy at Hamilton Marine in Portland).


tja,

Pressure treated plywood question: Are the XL pamels recommended for use as is on aluminum boats?

Alan

[August Ice]

Thank you Alan Your advice is highly appreciated. It turns out I also have to replace the deck and seats in the bow as well as part of the floor under the dash where there is a walk through windshield. I was thinking of Rhino lining it to make it washable after going out on the ocean. rather than putting carpet back on... Do you think Rhino lining appropriate or should I epoxy that as well?

Janet

[alan white]

I don't know if Rhino has an epoxy based or polyester-based resin, or if its polyurethane. I would guess epoxy or polyurethane, and if so, not a bad alternative to carpet, which I feel belongs in a living room and not on a boat. The surfaces the "lining" is applied to should be sanded and clean.
Expensive, I imagine, and so it had better be a good product with a guarantee. I'm not too familiar with Rhino-lining on boats or trucks.

Alan

[tja]

Hello, XL panels made by Greenwood products are used both in aluminum and fiberglass boats. It is guarenteed for life including labor last time I read there web site. Sincerely, Tom.

[alan white]

Thanks, Tom. Labor too? ... they appear to be working hard to overcome some prejudices people have about pressure treated plywood of the construction variety.

A.

[tja]

Hello, I went into Greenwood's web site and they have changed it some what. It isn't clear if they cover labor any more. Last time I was at there web site they said they hadn't had a failure of rot or delamination in the product since it's inception. I've used the product and was very impressed with the quality. Other then color and some extra weight you can't tell any difference from regular plywood except for it's obvious better quality in streightness , surface, and lack of voids.Sincerely, Tom.

[August Ice]

Has anyone heard of Lauan marine plywood?? My supplier is having delays getting Okoume or Maranti.

[alan white]

You could use fir or phillipine mahogany (lauan). Lauan is fine, so long as it's made with marine-rated glue.

[USCGRET/E8]

I would use (as I have) Interlux Interdeck. It's a (one part)Polyurethane Non-skid Finish for decks. It's a bit pricey at $35 a quart, but a higly rated product. Comes in 5 colors. Check it out:
http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/66496/377%20710/0/Interlux%20Interdeck/Primary%20Search/mode%20matchallpartial/0/0?N=377%20710&Ne=0&Ntt=Interlux%20Interdeck&Ntk=Primary%20Search&Ntx=mode%20matchallpartial&Nao=0&Ns=0&keyword=Interlux%20Interdeck&isLTokenURL=true&storeNum=null&subdeptNum=null&classNum=null

[PAR]

Mercanti, lauan and Philippine mahogany are all one and the same material (sort of). It's a conifer (evergreen) that happens to look somewhat like mahogany (some of it and to an untrained eye). You must be careful about these woods, as the quality, species type, construction methods and adhesives used must be questioned, from this part of the world. It's long been well known, that lumber and plywood coming out of the lower western rim countries can be dubious and possibly mis-representative of what you actual get. Stick with well known importers.

[August Ice]

Thank you Par... I persisted on the Maranti BS1080 and as it stands they can only get 1/2 " and 3/8" Maranti so we'll end up using 2 of the 1/2 and 1 3/8 to do the transom and 1/2 " for the decks and seats. The 3/4 " was luaun.

Janet

[August Ice]

Thank you Alan for the Hamilton Marine connection.. We went there Monday... Great prices and selection.

Janet

[alan white]

Glad you found them. Did you end up getting the ply from that guy in Yarmouth? I've never dealt with him, but I'm sure I will one day soon.

Alan

[August Ice]

I've only talked to Katie over the phone so far. I shared some information on Okoume and maranti plywood that I found on a website www.boatbuildercentral.com and specified that I wanted Maranti BS 1080. She was very informative regarding the 3/4 " being Luaun exterior ply She's always willing to go the extra mile to get the right stuff for her customers. My ply will be arriving Tuesday. That will be my first time there. The Maranti BS1088 is about $97 for 4x8x1/2" but the other Maranti was $ 48 same size. Okoume was $148 for the same stuff but their supplier was having a tough time getting it in stock.

Janet

[PAR]

A tip for your transom, to make it stronger without any extra fuss, is to cant the grain each way as the plywood goes in. This increases cross grain strength considerably (the manufactures do it too). Each piece of plywood has several veneers making up it's construction. This produces grain running side to side and also at 70 and 110 degrees, which increases the cross grain strength fantastically. In fact, the ideal way is to cant it as much as you can, in your case 22.5 degrees would be ideal, but you might run into difficulty with the sheet not being big enough to cover the whole transom in one shot.

Draw up a semi scale picture of your transom and a same scale 4' x 8' sheet of plywood. The first one goes on long grain (8' dimension) straight across, from side to side, then see how much cant you can put into the next two sheets before you run out of plywood. Yep, it does produce a lot of weird shaped waste, but it is surprisingly strong.

This sketch shows the two layers of plywood angled around 20 degrees, which in your case is three layers. Make the 3/8" layer the straight across one.

http://www.boatdesign.net/gallery/data/3172/medium/PAR-50.jpg

[August Ice]

Hello Par thank you for that tip.. I would've never known. It happens that there wouldn't be that much waste by looking at your diagram. We are also needing to replace the deck and seats in the bow, and under the dash. We could use some of the triangular pieces for the bow rider seats and compartment storage covers.

Janet

[PAR]

The arrangement shown above produces about 50% waste, which is considerable. I have many odd ball shapes stacked around here, hoping to find a use for them some day. It's not really waste, if it gets you back in the wet stuff, with a nice strong repair.