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Old 10 December 2005, 10:15   #1
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What happens to the

My question is what exactly happens to the transom when the boat leaves the water and lands? Is there a lot of stress/tension on the transom? Is "wave jumping" bad for the transom? Anything relating that....just tryin to do a little research
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Old 10 December 2005, 11:27   #2
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I have wondered that. There must be a helluva lot of stress, mustn't there?
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Old 10 December 2005, 11:51   #3
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A lot depends on how the engine is mounted. An inboard wouldn't be so bad but a twin outboard setup would be a different matter.

Not only is there the weight of the engines - about 1/2 a ton - pushing down but there is also a twisting force as the props suddenly find grip again and try to twist the top of the transom off.

Not only all that but also there is a lot of force coming up from the hull.

Just as well plywood is such an amazing material.
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Old 10 December 2005, 12:08   #4
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hmm i didnt even think about the force of the prop
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Old 10 December 2005, 12:57   #5
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Quote:
Originally Posted by codprawn
A lot depends on how the engine is mounted. An inboard wouldn't be so bad but a twin outboard setup would be a different matter.

Not only is there the weight of the engines - about 1/2 a ton - pushing down but there is also a twisting force as the props suddenly find grip again and try to twist the top of the transom off.

Not only all that but also there is a lot of force coming up from the hull.

Just as well plywood is such an amazing material.
No probs Cods. That's why if you are using twins - you go for a RIGHT and LEFT engines- you can counter a lot of the torque generated. My transom is still there despite some serious abuse by the driver....

Jonathan
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Old 10 December 2005, 12:58   #6
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Quote:
Originally Posted by codprawn
A lot depends on how the engine is mounted.
I reckon how the boat is moulded is probably more important!


Quote:
Originally Posted by codprawn

Just as well plywood is such an amazing material.
Not always! Marine ply is pretty amazing, shuttering ply isn't, but either is only partially responsible for a decent transom! The laminates that it's contained in is more important! Quite alot of high perf outboard boats now use foam for the transom, with ply being used for the o/b bracket footprint, so as to prevent the mounting bolts from crushing it.
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Old 10 December 2005, 13:10   #7
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Quote:
Originally Posted by Chopppywaters
My question is what exactly happens to the transom when the boat leaves the water and lands? Is there a lot of stress/tension on the transom? Is "wave jumping" bad for the transom? Anything relating that....just tryin to do a little research
Yep, can be really bad for the transom, that's why you "must" always follow the RIB manufactures recommended outboard weight/power figures.

I am currently waiting for repairs to my transom for exactly those reasons....Two 4" cracks across the top of my transom knees and fibreglass that has lifted away from the back of the wood core.
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Old 10 December 2005, 15:02   #8
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Originally Posted by eupa
No probs Cods. That's why if you are using twins - you go for a RIGHT and LEFT engines- you can counter a lot of the torque generated. My transom is still there despite some serious abuse by the driver....

Jonathan
I wasn't on about torque - I am on about the thrust when the props suddenly enter the water - so unless you have one going full forward and the other going full astern....
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Old 12 December 2005, 04:53   #9
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Quote:
Originally Posted by Dirk Diggler
I reckon how the boat is moulded is probably more important!




Not always! Marine ply is pretty amazing, shuttering ply isn't, but either is only partially responsible for a decent transom! The laminates that it's contained in is more important! Quite alot of high perf outboard boats now use foam for the transom, with ply being used for the o/b bracket footprint, so as to prevent the mounting bolts from crushing it.
Our raceboat uses a foam / marine ply transom, both materials are laminated with fibreglass between each layer - the design of the knees and other support for the transom is responsible for transferring the stresses to the hull, and these can fail if designed or built incorrectly as well .............
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