transom height question (replacing transom)

[Keithwpg]

I am going to replace the wood section of my transom on my older areoliner boat, the back side (water side) of the transom is all aluminum and it appears that there is just a 1 inch thick piece of plywood as support on the inside. the plywood does not go right to the floor it is about 6 inches off and it sit on a "lip" but it is the full width. this plywood is bolted to the transom in a few places. the motor appears to be sitting too low and the previous owner looks to have tried to remedy this by adding a spacer which is getting weathered. the way i see it since i am replacing the plywood i can make it taller to get the motor up higher where it should be.

i have 2 questions

what height should i put the motor at? i know the cavitation plate should be right around the bottom of the boat but what pin should i put the motor at to measure where the plate is now and determine how much taller the transom should be. i took 2 pictures to show the different angles.

since the plywood really isn't sitting in any water at all what should i use to seal it up?


here are some pictures. i hope that makes sense

 

[ezmobee]

Re: transom height question (replacing transom)

That lower plate is supposed to be even with to an inch or so above the keel. Looks like you might have a long shaft engine on a short transom (cuz even with that spacer you're still too low). You could raise your transom but if it was mine I'd do something more along the lines of this http://forums.iboats.com/showthread.php?t=321432

Seal your new wood with epoxy resin and then paint it.

 

[Keithwpg]

Re: transom height question (replacing transom)

raising the transom on this boat just seem like it would be easier to me. i'm already taking that old plywood out, seems like i could just cut it an extra few inches taller?

 

[ondarvr]

Re: transom height question (replacing transom)

Yes you can cut it taller, you need to some additional support though. If the motor is raised much more the top clamp will right at the top of the existing aluminum hull, so use some aluminum in there too.

 

[Keithwpg]

Re: transom height question (replacing transom)

ok im completely new to epoxy and such so i kinda shy away from it for now. since the wood is not actually submerged in the water and it looks like the plywood that was in there is about 20 years old and is still in decent shape (still needs to be done) could i just use something like this to seal the wood and then paint it? even if it only lasts 10 years or so


http://www.recochem.com/en/products...od_preservative/item/clear_wood_preservative/

only reason i ask is cause from what i can see this ply wood isn't touching the floor of the boat and will see about as much water as say a fence or deck would (the back side of the transom is aluminum)

 

[Ike-110722]

Re: transom height question (replacing transom)

You could but it would be nowhere near as good as sealing the wood in epoxy. Epoxy not only seals the wood it stabilizes it so it doesn't expand and contract with the amount iof moisture in the air. Epoxy is easy to use. You get two part, A and B. Depending on the brand and type you mix the two and brush it on (you can use a roller too) Just follow the instructions.

 

[sublauxation]

Re: transom height question (replacing transom)

Here's what I did to mine: http://forums.iboats.com/showthread.php?t=412704&highlight=sylvan+splashwell
If you keep the same shape and are careful when removing the top cap you may be able to save it. I had to have new metal bent and welded to shape but it wasn't overly spendy. I also put a sheet of 1/16 aluminum across the inside of the plywood that tucked under the top cap to keep the water off it.

 

[Keithwpg]

Re: transom height question (replacing transom)

the ones i seen said something about fiberglass mat on the instructions. is that the right stuff and the mat is just optional?

also sublauxation that looks like something similar to what im doing and it is giving me some ideas. thanks!

is this stuff ok?

http://www.princessauto.com/workshop/hand-tools/automotive-tools/autobody/8204992-fibreglass-resin

 

[ezmobee]

Re: transom height question (replacing transom)

Keith, there are two types of resin: polyester and epoxy. Fiberglass boats are made with polyester resin and fiberglass. Poly is good stuff and is less expensive than epoxy but it has to be used with fiberglass. It has no real strength by itself. It would crack and flake off pretty quickly with no glass. The Bondo stuff you posted is polyester. Epoxy can be used with fiberglass but it can also be used by itself like a varnish. You will most likely need to order it online. Epoxy isn't UV protected though so you'd need to also paint it. If you don't want to mess with fiberglass or epoxy, a quality marine spar varnish would be next best. Porch and floor paint is an option as well (but probably not as good as spar varnish).

 

[bonz_d]

Re: transom height question (replacing transom)

Sorry but to me it appears to be a 15" transom with a short shaft Mercury. My 1984 Lund is the same way. 15" transom with a short shaft Evinrude and yes the cavitation plate is well below the the bottom of the boat when the engine is mounted directly onto the transom. Why they are built this way is beyond me. Have mine raised about a 1/2" with a spacer also and it is still about 1/2" below the stern. The difference between a short and long shaft is 5" and neither this one nor mine is 5" too low.

Keith, I would use the top hole/pin location on your boat. The lowest hole would cause it to nosedive and push instead of coming up to plane. Myself I would seal it with spar varnish on all sides or a number of coats of good marine paint after using a good wood sealer to closeup and seal the grain. I grew up in a time when many boats were make from all wood, plywood and planks, and they were not glassed or covered in epoxy and they lasted many many years. More work yes but beautiful to look at!

 

[Keithwpg]

Re: transom height question (replacing transom)

Sorry but to me it appears to be a 15" transom with a short shaft Mercury. My 1984 Lund is the same way. 15" transom with a short shaft Evinrude and yes the cavitation plate is well below the the bottom of the boat when the engine is mounted directly onto the transom. Why they are built this way is beyond me. Have mine raised about a 1/2" with a spacer also and it is still about 1/2" below the stern. The difference between a short and long shaft is 5" and neither this one nor mine is 5" too low.

from what i measured to make the cavitation plate even with the botom of the boat i would need to cut my new transom around 1 3/4 inch taller. would i still be ok doing that or should i just make it about 1 1/4 inches taller? im in the process of laminating my plywood so i wont be cutting anything for a few days.


also thanks fopr all the replies, it is helping me TONS!

 

[bonz_d]

Re: transom height question (replacing transom)

Keith I wish I had an answer for you but in all honesty I would just be guessing. As I stated previously I have no idea why the transoms are designed this way, so that it is actually too low. But Lund is a major manf. with a great reputation so there must be a reason for it. Just wish I knew! Some have said it provides better handling though less top speed.

How did the boat perform the way it was?

 

[Keithwpg]

Re: transom height question (replacing transom)

it seemed to preform pretty good, i think ill just raise it up and inch or so since there was a 3/4 inch spacer before. raising it an inch will still leave it about 3/4 inch below the bottom of the boat. i guess thats playing it on the safe side.

 

[bonz_d]

Re: transom height question (replacing transom)

I'm not a high performance, high speed boater though I do know that those who are use adjustable jack plated to fine tune the hieght of those outboards. Now neither your tinnie nor mine are anywhere near being High Performance!

 

[Keithwpg]

Re: transom height question (replacing transom)

ha ha definitely not a high performance boat! its for fishing only with the odd time pulling a tube, but i figure if im gonna be changing the height anyway i would just try and get it proper. i am gonna just raise it an inch and a bit so its still below the bottom of the boat just to be safe.

 

[bonz_d]

Re: transom height question (replacing transom)

Remeber to let us know how it works out, if you see any performance improvement. If so you can always add another shim afterwards.