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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

How thick is the transom?

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albert
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USA
262 Posts

Initially Posted - 12/23/2002 : 22:25:25

I'm going to upgrade my motor bracket. How thick is the transom of 1984 C25's? ie. How long should the bolts be? I'm going to add 2" of marine plywood for strength.

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

Edited by - on

OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 12/23/2002 : 23:48:15

Albert,
Don't spend the extra $ for marine grade plywood, especially if you're going to place it inside of the transom. The only difference between marine and exterior grade plywood is marine grade is guaranteed not to have any voids.
As for the bolts, why not just buy bolts two inches longer the ones you remove?
Good luck.

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albert
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262 Posts

Response Posted - 12/24/2002 : 02:31:37

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
Albert,
Don't spend the extra $ for marine grade plywood, especially if you're going to place it inside of the transom. The only difference between marine and exterior grade plywood is marine grade is guaranteed not to have any voids.
As for the bolts, why not just buy bolts two inches longer the ones you remove?
Good luck.
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

I didn't buy marine grade plywood for the interior. I bought exterior grade BC. I just didn't want to side track the discussion regarding wood types <img src=icon_smile_wink.gif border=0 align=middle>. Thanks for the suggestion though.

I've actually purchased a small and inexpensive piece of teak finished marine plywood for the exterior part of the support bracket.

I haven't removed the bolts. I wanted to get all the necessary gear before installation. My boat is 45 minutes away--45min going, 45 return=1.5 hours just to get to the boat (not including packing the car full of tools, etc.)

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 12/24/2002 : 09:04:04

"I've actually purchased a small and inexpensive piece of teak finished marine plywood for the exterior part of the support bracket." - Albert

I like Dave Bristle's idea of using starboard(available at most home center's) instead of plywood due to it's strength and no maintenace.

What type of motor mount are you installing?

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

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albert
Captain

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USA
262 Posts

Response Posted - 12/24/2002 : 10:40:39

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>
"I've actually purchased a small and inexpensive piece of teak finished marine plywood for the exterior part of the support bracket." - Albert

I like Dave Bristle's idea of using starboard(available at most home center's) instead of plywood due to it's strength and no maintenace.

What type of motor mount are you installing?

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Garelick, I forgot which model but its the one with 11.5" of vertical travel. Its rated for a 20hp engine and 120lbs.

How does starboard compare to plywood in strength?

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

Edited by - on

dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 12/24/2002 : 11:22:02

"How does starboard compare to plywood in strength?"

I would think that it is stronger than plywood since it is more dense. Additionally, if I were adding a backing plate I would probably use either a metal plate or possibly starboard instead of wood because when you start torquing down the mounting bolts, the washers may start digging or crushing into the wood. When I built a wooden gate in the backyard I had to be careful not to tighten the bolts to much because the washers would sink into the wood. To check this out, thread a bolt into a piece of marine plywood and tighten it down with a couple of wrenches and see if the plywood holds up.

Check out this link at King Starboard.

http://www.kingstarboard.com/main.php?link=starboard.htm

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/24/2002 : 12:32:51

Half-inch Starboard has PLENTY of strength--it does not compress. I used it inside and out because I had enough on the 2'x4' board I bought. 2" of plywood (1" on each side?) is overkill. Because of its stiffness, on the concave curved interior, it'll put more stress on the fiberglass at the edges of the board. I rounded and tapered the edges of the inside plate to prevent that. You mainly just want to spread the load from the bracket base and interior washers over a couple of square feet, especially below the bracket on the outside.

Sorry I don't remember the length of my bolts...

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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OJ
Master Marine Consultant

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USA
4382 Posts

Response Posted - 12/24/2002 : 13:23:01

<BLOCKQUOTE id=quote>quote:<hr height=1 noshade id=quote>

I've actually purchased a small and inexpensive piece of teak finished marine plywood for the exterior part of the support bracket.

<hr height=1 noshade id=quote></BLOCKQUOTE id=quote>

Albert,
We're not trying to beat you up here - just sharing our experience. I would advise you not to use teak plywood for any exterior applications. I have found that the top lay of veneer is so thin that it just doesn't hold up - eventually the plywood starts to delaminate. Starboard is an excellent option.

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albert
Captain

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USA
262 Posts

Response Posted - 12/25/2002 : 01:13:39

Starboard it is! I believe I can still return my 2 x 2 piece of teak veneered marine plywood. My BC exterior plywood is a left over piece from another project.

What starboard thickness would you recommend? Is 1/2" enough inside and out?

Any idea what the transom thickness is?

Albert Iturrey
al@comhertz.com
Abacus': http://www.comhertz.com/abacus

Edited by - albert on 12/25/2002 01:19:23

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/25/2002 : 13:58:18

Albert... I think I had to use 3" bolts to go through two 1/2" Starboard plates and the transom (on the starboard side above the shelf at the foot of the quarterberth, where it's 2 layers with a foam core). But they may even be 4 inchers... I'd only go thicker than 1/2" if I needed it to move the bracket away from the transom. 1/2" Starboard is very tough stuff, but very easy to cut and shape.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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Jim L
Deckhand

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7 Posts

Response Posted - 12/28/2002 : 21:21:51

Albert,

The problem I had when I beefed up the outboard bracket was the fact that there is a gap between the liner and the transom. I had to use a large hole saw to remove the liner so I could access the transom. I used SS steel to reinforce the exterior, and plywood coated in epoxy on the inside. It worked for me.

Jim L.

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/29/2002 : 20:11:25

On our '85, the space between the liner and the hull at the transom is cored with foam. That combination should add to the strength of the bracket--not detract from it. If you put a backing plate on the liner, you should have no problem with compression. I split the internal backing plate to allow it to better conform to the slight curve in the liner. If you have no core between the two layers, I'd suggest installing a "compression tube" for each bolt by drilling each hole in the liner the diameter to match the diameter of a thick-wall aluminum tube, and then putting a piece of the tube in each hole so that it keeps the backer from pulling the liner toward the hull. But I could be over-engineering now... <img src=icon_smile_blush.gif border=0 align=middle>

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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