Transom replacement or design flaw?

[redneck joe]

Scott is smarter than me and the pic ain't great but that wood does not look healthy. For the small dollars to replace, start there.

 

[bikerider]

Alright, I'll replace the transom wood first. Then probably a water test. I will update this thread with the progress. It sounds like if I need something extra like a knee I can add that later.

 

[airshot]

The flexing made me think I might develop cracks or a break if I went much beyond half throttle. I already have the plywood for new transom wood. I still need to research more about adding a knee, but I'm assuming it would have to be welded in. I also saw an aluminum plate that goes between the transom and outboard. I have linked it below.

Transom Engine Mounting Bracket - Standard 1.75" Thickness - Tiny Boat Nation

Custom Outboard Mounting Bracket - Transom Wrap 1/8" Thick Aluminum Transom Bracket to securely mount your outboard and reinforce the critical part of your transom. Designed for the common jon boat and V-Hull transom at 1.5 to 1.75" Thickness. Extra Wide 2" available for thicker transoms. 11"...

tbnation.net

Have saw many rebuilders just add an aluminum piece between the rear of the tank seat and then to the transom riveted or screwed in place to stiffen the transom. Back in my younger days, made a few myself, then no holes thru the bottom !

 

[cyclops222]

Your stern was built to cheaply. You are now a designer. Post some / a lot of pictures of top, outside showing the rivets, thickness of the transom top, how far down the inside of plywood extends.

My gut instinct says we do a complete redesign to spread out the thrust to the very corners of the hull sides. Not difficult just grind off all the RIVIT heads from the inside. So we get a flat surface to do a FULL shape inside hull plywood piece. We can trace the shape by clamping the rough cut piece on the outside of the transom. The a series of pop it in and out on the inside until you have about 1/ 2 clearance on the bottom and sides.
Corner braces will require notching out also.
No difficult. Just fitting in and cutting. ANYTHING you do will be capable of 20 hp. Thickness ? 3/4 would be ideal. but so would 1/2 with some sealant around the edges. Painting the final piece is O K. Then the sealant. Drill the empty rivit holes about 3/8" deep into wood. Put some dummy short rivit heads in with sealant.
SCHAZAAMM

 

[Scott Danforth]

Not needed. Rebuild existing transom with AC. Plywood, make sure wood goes to the edges. Laminate the two pieces with tite-bond III.

Seal the wood with Rust-Oleum

Drop in place, replace the transom cap

 

[airshot]

We need to remember that this is only a 12' aluminum rowboat, a basic model from Starcraft. Max HP rating is 10 hp, and that was probably rated with a lighter weight two stroke. Replace the old wood with some good plywood and the boat will be better than new !! Most all small row boats have some flex in their transom when a motor is added......

 

[jimmbo]

A Strip of Right Angle Aluminium along the Board bolted thru the Transom will certainly stiffen it, another along the Top of the Transom, would also raise the motor a 1/4" or so too

 

[MikeSchinlaub]

As small as that transom is, I like the idea of a brace. Maybe one on each side? Maybe bolted to the bottom if there is a good rib running across, or riveted to a strong point on the bottom. Through bolts on the transome with some big washers.

 

[cyclops222]

DO NOT BOLT the flattened end of the brace to the THIN BOTTOM SKIN of the hull !!! It will flex and break thru that thin skin very quickly.

 

[bikerider]

DO NOT BOLT the flattened end of the brace to the THIN BOTTOM SKIN of the hull !!! It will flex and break thru that thin skin very quickly.

What do you think of this?

Transom Engine Mounting Bracket - Standard 1.75" Thickness - Tiny Boat Nation

Custom Outboard Mounting Bracket - Transom Wrap 1/8" Thick Aluminum Transom Bracket to securely mount your outboard and reinforce the critical part of your transom. Designed for the common jon boat and V-Hull transom at 1.5 to 1.75" Thickness. Extra Wide 2" available for thicker transoms. 11"...

tbnation.net

 

[bikerider]

These are some up close pictures of the transom wood. The wood is definitely de-laminating. The last one is a picture of the tray after I removed the original wood.

 

[MikeSchinlaub]

Does your motor clamp on or bolt through?

 

[bikerider]

Does your motor clamp on or bolt through?

Clamp on.

 

[jimmbo]

Actually that plywood doesn't look as bad as a lot I have seen. I will assume that the Boat was from the 70s, maybe early 80s, so 45+ years.
Another piece of Marine Plywood, will probably outlast most of us on this Board
Doubt there is any Advantage to adding a Knee, if 5hp is all you plan to use

 

[MikeSchinlaub]

Ok, if it's just a tiny little 5hp like jimmbo said, that's just overkill. You could just get some flat stock to act as one big washer and call it a day.

The reason I was asking about the mount though. If it's a bolt through, you would have to drill through and seal between the plate and transom on both sides. Since its a clamp, some big screws, say 14x2 wood screws, through the top to hold the plate to the transom would probably work and be easier to seal.

But again, overkill for a little motor.

 

[bikerider]

Actually that plywood doesn't look as bad as a lot I have seen. I will assume that the Boat was from the 70s, maybe early 80s, so 45+ years.
Another piece of Marine Plywood, will probably outlast most of us on this Board
Doubt there is any Advantage to adding a Knee, if 5hp is all you plan to use

I think the boat is actually from the mid 90s. The reason I posted is because even with the 5hp outboard, I was getting a lot of transom flex. I don't want to replace the wood in the same configuration and end up with the same transom flex. That's why I was asking about a transom plate.

 

[bikerider]

Ok, if it's just a tiny little 5hp like jimmbo said, that's just overkill. You could just get some flat stock to act as one big washer and call it a day.

The reason I was asking about the mount though. If it's a bolt through, you would have to drill through and seal between the plate and transom on both sides. Since its a clamp, some big screws, say 14x2 wood screws, through the top to hold the plate to the transom would probably work and be easier to seal.

But again, overkill for a little motor.

I just don't want to end up redoing the transom in the original configuration to have the same problem with transom flex. Can you elaborate on the flat stock you mentioned in your post?

 

[jimmbo]

How much HP is the Boat rated for?

 

[bikerider]

How much HP is the Boat rated for?

10 hp maximum.

 

[jimmbo]

What do you think of this?

Transom Engine Mounting Bracket - Standard 1.75" Thickness - Tiny Boat Nation

Custom Outboard Mounting Bracket - Transom Wrap 1/8" Thick Aluminum Transom Bracket to securely mount your outboard and reinforce the critical part of your transom. Designed for the common jon boat and V-Hull transom at 1.5 to 1.75" Thickness. Extra Wide 2" available for thicker transoms. 11"...

tbnation.net

People use those to buy time on a Fiberglass boat with a Rotted Transom

"I think the boat is actually from the mid 90s. The reason I posted is because even with the 5hp outboard, I was getting a lot of transom flex. I don't want to replace the wood in the same configuration and end up with the same transom flex. That's why I was asking about a transom plate."

This flexing you saw with the 5 hp, was before you took the old Transom out, correct? The New Transom will likely have No or very little Flex, as the Plies in the Plywood are glued into one piece

The Cap that is cracked... Myself, I would get a Strip of Metal wide enough to just fit inside Cap and Epoxy it to the Cap. That's what I would do to gain some Rigidity