Transom question

[vectorizer]

What wood should I use in the transom. Thanks Matt Ludwig

[hsbob]

plywood. 2pieces of 3/4 or 3 - of1/2 or thicker. each bonded to the tramson out as far as possible. bond each sheet with epoxy and mat. plus screw each sheet together with SS screws. make plans for a knee brace. epoxy not polester resin.

[Techno]

Marine grade. If your too cheap for marine then go with the higher grades of fir. C or whatever that crap is has a whole lot of voids in it and one side don't have patches. All construction grade ply has voids and bark filler, the reason for marine ply is it have either. Its solid veneers that are butted together.

And after you've finished the transom never drill a hole in it without sealing said rot highway.

[vectorizer]

Thanks for replies.

[Trikki1010]

What Techno says it true, Marine Ply is rated so there are no voids in the wood and the wood utilized meets certain criteria.....

But,

If you do use regular plywood, make sure it is 5 ply, not 3 ply spruce and that it is sanded on both sides. By the time you get there, Marine Ply isn't that far off from ACX (A=Sanded Nice C=Rough finish X=Exterior Glue )

[Riverratt]

I thought I read somewhere that fiberglass does not stick very well to marine plywood.:confused:

[sho305]

Does not stick to treated wood, like wolmanized. Treated is also pressure cooked in the solution, IN the solution as in boiled so it is very wet and would have to be dried. It will still rot in a boat so there is little point for using it for major areas. Might maybe work better for a dash/seat or something that dries if it gets wet.

My epoxy bonded to the ply no problem, and I glassed it in the boat within 24hours to get a chemical bond to the new glass. To a point the wood is still a core and should be held in the boat by much more than the surface bond. I had the old glass channel on the edge that the new wood fit in, then I added more. I glued two pieces of ply together on the smooth side and it broke the wood not the epoxy. Heck I glued plastic together with it once.

Marine ply is very high quality like the best furniture ply. I used cheap CDX in my bayliner and it worked great with epoxy. The voids don't affect strength really unless you mount into one/etc. I beefed it up from stock, and I figured if any water ever got in any wood would rot so why bother. With a nicer boat I would reconsider. It is very stiff now. I painted the wood parts with epoxy 4 times until they were sealed before installing/glassing them in the boat. I used 5200 on the motor bolts after I glassed those and the drain inside the holes, so even if they leak no matter unless they get crushed from over tightening.

Good wood is good wood, but IMO sealing the living blank out if it is more important than anything else. IMO I would use wood of quality comparable to the boat and the use it will have to fullfill. If it is highly stressed you better use the best.

[Techno]

I thought I read somewhere that fiberglass does not stick very well to marine plywood.:confused:

:rolleyes: fiberglass don't stick to nuthin. Its the plastic that does all the stickin.:eek:

[Naiscoot]

http://www.transomrepair.com/index.html

I was recommended a product called Sea Cast. My mechanic has used it and swears by its strength. Naiscoot

[riverrunner114]

this is another one of the dead horse debates...but I have built and installed with zero returns several hundred transoms ..built with bc plywood and polyester resin....but there are those that will say that wont work:)

[Naiscoot]

John, How much for a typical bass boat transom rebuild? The reason I ask is my mechanic has been using the seacast system and it is cheaper than the total wood rebuild. The savings is in the labor. Thanks, Naiscoot

[riverrunner114]

depends, of course..but in the thousand, fifteen hundred range...if there is no metal flake repairs of course... he he ... those are charged by the hour....

[86vintage]

To pay extra money for marine plywood over the cost of nonmarine plywood is "money well spent" knowing that you did the job "right"http://forums.screamandfly.com/forums/images/icons/icon14.gif
if you have the extra $ 100.00 do it with marine plywood, it will be stronger. Yes you can do it with other plywood grades but it will not be as strong. This is now is your decision. so did i make 5 shots or 6?

make the right decision

James
86vintage

[riverrunner114]

In concept I agree that the better the materials the better the job. However when I build a transom, there are no voids. Every boat is different and so are the demands placed on each one different. These have to be taken into consideration when building structure in a hull. My warranty is for the duration you own your boat. And zero failures so far speaks for itself. I take alot of pride in the amout of effort that goes into all of my work and do not intend on reducing that quality anytime soon. 90% of the 'home repairs' I see have failed not due to poor quality of materials, but more to the lack of understanding of what it takes to build a rigid and watertight transom. If you really love your boat and insist that it be done right, take my advise and take it to a professional that does this sort of work for a living. Ask about thier warrenty. I really try to stay away from doing hull work anymore, I prefer to work on the black box on the back. Tired of itching:) . But if you are insistant on doing the work yourself, I would invite you to PM me with any of your concerns, problems or ideas. If not me, there are many qualified fiberglass guys here on this board. Just because we all have different plans of how to get there, its the finished product that is important. there is a huge amount of knowedge on this site and that is worth its weight in carbon fiber:) Good luck, john

[Jeff_G]

I too have done many, many transoms in my 32 years in the business. From race boats to Bayliners. In most cases I use CDX exterior grade plywood. The plywood is only a core, nothing more. If properly done it will last as long as the boat.
Marine grade plywood uses the same glues as regular exterior grade. The big difference is the final exterior layer is usually an exotic hardwood like mahogany. If you are concerned about looks then that is the way to go. But with most transoms which are painted it just costs more. There really isn't any difference in strength.
Pressure treated plywood can also be used as long as the moisture content is below 60%. Dryer is better. A cheap moisture meter can be had for about $15.
Whether you use epoxy or poly depends on your bank account and how the boat was initially made, and additional repairs/modifications. Either one will have a mechanical bond as opposed to a chemical bond. With proper preparation either will work fine.
One trick I do is I cut slots in the wood before I glass with a circular saw. Just small 2-3" will do. When the wood is sandwiched with a layer of mat and resin between the two pieces the resin will fill the gaps from the slots and act like a fastener. The two pieces will be permanently bonded and much stronger than without.
Just my 2 cents but if apperance is not in question then I use normal plywood.

[riverrunner114]

I too have done many, many transoms in my 32 years in the business. From race boats to Bayliners. In most cases I use CDX exterior grade plywood. The plywood is only a core, nothing more. If properly done it will last as long as the boat.
Marine grade plywood uses the same glues as regular exterior grade. The big difference is the final exterior layer is usually an exotic hardwood like mahogany. If you are concerned about looks then that is the way to go. But with most transoms which are painted it just costs more. There really isn't any difference in strength.
Pressure treated plywood can also be used as long as the moisture content is below 60%. Dryer is better. A cheap moisture meter can be had for about $15.
Whether you use epoxy or poly depends on your bank account and how the boat was initially made, and additional repairs/modifications. Either one will have a mechanical bond as opposed to a chemical bond. With proper preparation either will work fine.
One trick I do is I cut slots in the wood before I glass with a circular saw. Just small 2-3" will do. When the wood is sandwiched with a layer of mat and resin between the two pieces the resin will fill the gaps from the slots and act like a fastener. The two pieces will be permanently bonded and much stronger than without.
Just my 2 cents but if apperance is not in question then I use normal plywood.

finally another real fiberglass guy, thanks Jeff... I too cut slits in my layers with the skill saw.. about 1/4" deep and about 2 inches apart...on all but the final outher layer.... it also assists you in forming any curvature that the hull may have....good luck john

[sho305]

My little bayliner only had one layer of 3/4", but is only rated at 90hp too and has a knee near the motor plus it angles there on each side...so the center only is wood. The clamp/well section is doubled up and encased in glass, that was ok. Anyway I put an extra layer of glass over the inside as it was real thin there but had about 1/4" of chopper on the edges that I left, and also covered into edges with new. I jumped on the motor so hard trying to check strength I bent the cav plate, and its pretty thick on the force. It don't move with CDX. I did it mostly for practice/learning, but the stock transom did last 20 years in it so I didn't see much point in doubling it up since I was not going to overpower it. I had hoped to sell it...

I used the epoxy because of the wood being in the center of the transom, it was more like a repair that way instead of replacing the whole thing. That stuff rules as far as stick, and it didn't cost that much. I got some on bare dirty untouched gel and it tore a piece of it out when I knocked it off. I cut the skin, something I would not do again, and layered woven about 4" wide into the ground tapered out cuts. I used SS deck screws to hold the skin on the wood and left them in, countersunk. I expect the rest of the boat to be long gone before the transom. I posted pics of the process in a thread called something like 'bayliner transom' in the glass section a few years back.

[Jeff_G]

John if you want a real strong transom cut the slots with a circular saw so the slots are beveled, all the way through. Cut just deep enough to go through. This created a mushroomed shaped slot that when it fills with resin is impossible to separate.
I grind out all the old wood from side to side. Grind the old glass and lay in some mat, plywood, thin layer of mat, the other piece of wood and followed up with more glass to encapsulate everything. I use SS screws to clamp the wood to the existing transom and each other.
I can guarantee you if done right it will last as long as the boat.
The biggest reason for transom failures are holes and screws driven and not sealed causing water intrusion.

[1BadAction]

I'm not a big fan of regular ply (although I have used it on larg projects). Marine ply is much nicer to work with, cuts better, looks nicer, stronger, and has better screw pull-out strength. Oh, and try mounting something to a knee in a tight area where there is a knot, what a bitch that is.

Like these guys said though, no matter what kind of ply, as long as its sealed up and water doesnt get to it, should last forever. I like a good QUALITY polyester, the boat is built with it and has lasted this long, also with the new weaves of glass (biax and triax stitch mats, carbon, etc) its going to be stronger even if it is built the exact same weight. JMO.

[sho305]

When I got my wood in there was an air slot down the sides where it fit in the old hole/slot. I glassed the inside and outside, then I drilled holes in the top and poured resin in to fill it up. The void had glass I put in there but it didn't get wet until I poured it full, I could see it in there through the glass. I think they choppered it and it didn't go into the corner or something as it was that way factory, but not now. I'm not sure it made a whole lot of difference, but I filled up. The wood fit tight, no way could I have made it larger.

[SandSled]

I'm staying away from seacast. If it was that good a lot of manufacturers would probably use it. It's heavier than wood, much heavier than composite. Go really good fir or marine ply.

You could also go composite with Coosa board / Penske board and the like....

[sho305]

From what I read it's just resin, glass, and filler. It is heavy and expensive. You still have to dig all the bad wood out. I guess it depends on the boat, if it is high performance and how hard the transom is to get at. Cheap old wood still has some of the best perfomance characteristics for boats, thats why they still use it. Like I said, that bayliner transom was just a piece of 3/4 cdx choppered over and it lasted 20 years. The guy I bought it from left it in the water all summer every year. If the motor bolts had been sealed it never would have rotted...and it had a newer shortblock in it, how much you bet they took the motor off and didn't reseal it. Might have been bad anyway, that is original motor and you need to reseal them now and then. It had that putty stuff on it. I would guess the 5200 lasts longer. I did have to strap the motor up on the way home, I thought it was going to fall off it was so shot.

[Techno]

If you want to think the plywood is a core I suppose cutting your structural member is OK but since it ain't no core I really don't suggest cutting into it just to create a better mechanical bond between 2 structurally destroyed parts. You've just cut the thing that makes the strength. Sanding it more than enough creates a mechanical bond for epoxy. I understand this is only 1/4" but its actually 1/2" out of 1.5" this is 1/3rd the thickness.

Just how many layers of glass are being put on 1.5" of plywood to turn it into a core?

I have to add that the only diff between exterior grade plywood and marine ply isn't the pretty cover but the interior. Look at the edge of both and you can see the difference. One has holes running through it and funny looking wood called 'bark' and the other has no holes and has whats called 'wood'

[sho305]

There was no bark in my CDX, just a little knot here and there and they don't fill them on the inside. I also made floor panels and seat bucks for it and hit very few voids in all those cuts. Maybe there are different grades I don't know, but to each their own use what you want. It is a good thing there are no voids in honeycomb core or air bubbles in foam core...I could not tell what came out, but the original bayliner wood had the same number of plies.

If it has a reasonable amount of glass on it the ply is a core, but yes thick ply sure adds strength as well. What I meant is that you should have enough on there where it would take serious damage to delaminate it even if it didn't stick that well....and you would really have to screw up bad to make epoxy not stick. You want to glue something together; epoxy don't play. I've fixed all kinds of wierd stuff with it. You take prepared surfaces and it is just plain wicked.

If one wanted wicked ply you would glue the plies together with epoxy, if you could. I don't think it would be any weaker if you cut slots in it and filled them with epoxy, though at much thickness you would want to use a structural filler. I don't really see the need myself after having tested the stuff, but I am not a pro either.

[Jeff_G]

Techno, do you really believe what you write?

The plywood in a transom is a core material. Period.

That is not to say it doesn't add strength. It does. The whole point of the slots cut through the wood, which are about 1/16" btw, are so the resin can fill these slots and give MORE strength and rigidity, not less. You are not structurally destroying the plywood, where did you get this?

Exterior grades of plywood are graded on the finish of the exterior plys and the number of knots and voids and how they are filled. There is no bark in any plywood. If there is the manufacturer is not meeting the industry standards.

Virtually all structural plywood made today uses waterproof phenolic resins which maintain the bond during moisture exposure.

At a difference of $18 per sheet for construction grade vs $85+ for marine, I can spend my money elsewhere.

Final question, how many transoms have you replaced in the last 30 years?

[86vintage]

From a production stand point yes the money can be saved and spent elswhere. From a purist level of one person doing the work himself. That person needs to make the call themselves.
If I were person is doing a Bayliner to fish with on a lake, save the money
Vs Myself who wants to try to break 100 mph with a fully built up Merc 2.5. and scream it threw the air on the ocean. I will spend the money, the extra $67.00. I know the job is right and the strongest it can be.
I wont be worried out on the water pushin the boat for all its worthhttp://forums.screamandfly.com/forums/images/icons/icon10.gif
As far as the guys that have done 100s of transums, yours will probably be stronger than mine, even though I used Marine grade and spent the money, because you have done so many, and I have not - but I know I did the best I could with the best materials available.

James -86vintagehttp://forums.screamandfly.com/forums/images/icons/icon14.gif

[RBT]

Poly has horrible mechanical bonding properties when compared to Vinal or Epoxy. I agreed with the CDX, though I do like Marine wood such as Okume or Meranti. There is also a company called XL who makes a pressure treated marine plywood... that resins will bond too. There are also compsites such as coosa and spaceage that are suitable, though I am still a firm beleiver in wood transoms.
As far as the wood being a core...... yup, my transoms are 1/2 Okume, 1" Balsa and 1/2 inch Okume. I have had boat with pure balsa transoms that wer perfect. As a matter of fact I had to remove a 1977 balsa transom last winter to change the motor ( in a stern drive Challenger 21 ). The only reason was the boat had 3-4 different drive/exhaust configurations an the transom was swiss cheese... water migrated no more than 1/3 of an inch. Balsa if correctly done will not allow lateral water migration.... unlike plywood. In theory.... you don't even need to seal balsa transoms for motor bolts........... That ought to get some negative responses.
Also I thought that is should be mentioned that Epoxy, unless post cured has no better mechanical bonding properties than a good etching vinalester resin.... and that is has greater cost, some health issues from some people and is a one way street for later repairs.

RT

[1BadAction]

showoff. :p

I just bought another sheet of 1/2" okume friday. price went from $48 2 years ago, to $78 :eek: I almost feel bad putting carbon over top of it, its so pristine.

[RBT]

ya well I just re-read what I wrote and the spelling a grammar is atrocuois........ and I am too lazy to fix it.

[1BadAction]

speaking of vinylester... whats the deal with ame 4000? I am down to my last gallon, can i still get it?

[RBT]

AME up here.... no, we can only get 5000. We have all swiched over to Hydrex 100 and 100HF for infusion. The laminators seem to like it a lot better than the AME 5000 too.

RT

[1BadAction]

cool... I'll check that out when I build the next one.

[Techno]

I'm totally confused now.:confused:
So what your saying is vectorizer doesn't need to bother changing his wood transom since it is simply a core on an outboard powered boat and don't matter how weak it becomes since its a core? As long as the skins are still strong the core won't matter a bit? why can't he simply add more glass to the skins and forget all that work and expense?

Theres your answer no need to replace this wiggley rotted stuff. Put your time and money into something else... like 100 more HP:D

At least I'm assuming his boats an OB.:o

[sho305]

The skins of a composite do supply the strength, but only as long as they are bonded to the core. That is why weak foam can be a core in a strong composite. A plywood core is just stronger yet allowing you to make a thinner composite. That is why end grain balsa is so good, because the end grains hold the skins nicely, and that is all the core needs to do. The skins make the strength of the panel and the core just holds the skins. That is oversimplified, but the jist of it.

In other words, if you took two plates of steel...and stood little trim nails up on end on the first every inch or so and then placed the second panel over it and could weld both ends of the nails...that would make a pretty strong composite panel even though you only had skinny little nails in there.

Once the bond is gone, you only have the strength of the panels alone. It is kind of like a truss holding up a roof, if you take the connecting supports out it is much weaker and falls in. It would take much larger wood to span the roof without the triangulated braces.

[carhartt981]

In my liberator 21' I used coosa board bluewater 28 in an 1.5" thickness. The transom is a full 2 5/8" thick. The problem with a composite is for a 4'x8' sheet its 600 dollars. But on the good side if the transom cracks again it won't rot out. I had seacast suggested to me, but i told them to get bent. Seacast and 100+ mph dont mix. Whether its marine plywood or a composite material, it pays to spend the extra and do it right. Just my 2 cents