Transom

router343

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Jun 9, 2008
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I have to replace the wood insert in my transom. My motor has the 25" shaft which sits to low in the water and i already have it mounted in the highest holes. My question is instead of cutting out the 5" drop down can i just leave it straight across and drill my new holes higher to get the motor a few inches higher inches higher.
 

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HotTommy

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You should measure the distance between the mounting holes on the engine and where the engine mounting bracket rests on the transom to be sure you don't mount the engine too high. You may need to leave a small cutout, or not.
 

clemsonfor

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I will second and third what the other guys are saying. Modify it to suit your needs. this is not really a high performance hull where minor tweaks may wreck some other form of its performance ability.
 

clemsonfor

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Another thing, I have never understood why some pontoon manufacturers would put a wood insert in the transom, it sits in the water on a boat that is always in the water and even on a boat that is always trailered why would you put wood on one of the most stressed and exposed to water places on the boat. I know wood is very strong for its dimensions but there is so much aluminum in the boat already why not just put a thick aluminum plate there with some heavy duty box aluminum for strength?
 

router343

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I like the idea of aluminum much better. Three questions.
1. Which grade of aluminum plate would you recommend?
2. Should it be the same 1"3/4 thickness of the wood?
3. Does it have to be welded instead of bolted?
 

router343

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Jun 9, 2008
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The motor is a 1996 120 HP Force extra long shaft (25"). I don't have the the manual with me at the moment but I believe it list the weight at 320 lbs give or take.
 

HotTommy

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One online hardware seller prices a 24"x24"x0.5" plate of 6061 aluminum at about $309. And I suspect it would take more than one 1/2" plate to stand up to the repeated "can opener" like flexing torque the engine produces. That is likely why manufacturers use high quality, water resistant wood instead.
 

ahicks

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Thought behind the wood may be it cuts down/eliminates much of the potential harmonics transferred from the engine to the boat.

Later model boats do have all alum. transoms that use heavy wall alum. tubing to handle the power/torque/twisting action imparted by the engine. The ones I've seen were all welded.

I would get some dimensions regarding where the cavitation plate is now with this set up, so you have some kind of target for this 25" setup you're going to. If you set the transom up so the cavitation plate is in about the same location (for starters) you should have something close. Might save a lot of head scratching later if things don't go so well on the maiden voyage....
 

clemsonfor

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One online hardware seller prices a 24"x24"x0.5" plate of 6061 aluminum at about $309. And I suspect it would take more than one 1/2" plate to stand up to the repeated "can opener" like flexing torque the engine produces. That is likely why manufacturers use high quality, water resistant wood instead.

I get that, but your probably looking at a retail price for a small end consumer like us. A huge boat builder is buying it whole sale by the semi load, and I think you can use that .5" piece in conjunction with some larger tube or some other support pieces to hold the engine up, I think that's how mine is. Its maybe .5'' or less plate and then some square tube or something that is welded into the sides? I don't remember. But I'm sure it is still cheaper and easier to make up some wood ones and bolt in there and just have it easily serviceable by the boater for future replacement and cut out $500 on the thing.
 

clemsonfor

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Thought behind the wood may be it cuts down/eliminates much of the potential harmonics transferred from the engine to the boat.

Later model boats do have all alum. transoms that use heavy wall alum. tubing to handle the power/torque/twisting action imparted by the engine. The ones I've seen were all welded.

I would get some dimensions regarding where the cavitation plate is now with this set up, so you have some kind of target for this 25" setup you're going to. If you set the transom up so the cavitation plate is in about the same location (for starters) you should have something close. Might save a lot of head scratching later if things don't go so well on the maiden voyage....

My 1997 Crest II has an all aluminum transom, like I was trying to explain why many builders didn't use it to begin with. I have plate and aluminum tube for the transom. My boat is not really a "late" model (1997) as I would call it, but is newer than many of these ones from the 80s still running around.
 

ahicks

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My first 'toon was a brand new '77 24' Crest that "featured" an adjustable height transom. New only because used pontoons back then were pretty much non existent (WAY before the current 'toon popularity existed). The boat I did the major reno. on last year was a '99 Suncruiser w/wooden transom insert setup similar to the OP's boat.

Point being, you're right on the money. My first thoughts generally gravitate to the older stuff.....
 

router343

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Jun 9, 2008
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My boat is a 21' Sun Tracker Fishin Barge. After looking at it again, I dont think the steering cable will allow me to go any higher, so i think i will need to search lower unit with 20" shaft or remove the 5" spacer and swap the water tube, drive shaft and shift shaft to 20" setup. Will need to find used shafts, they are to expensive for such an old motor.
 

ahicks

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I would add that the Chrysler engine line is not all that popular to start with, making them pretty inexpensive. My bet is you can find an entire engine for less than the price of the parts needed to go from 25 to 20".

You're pretty sure that steering cable can't be removed and rerouted to accommodate your plan with the 25" engine?
 

Cat nip

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Jul 25, 2015
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From your picture it looks like the wood for the transom was cut down at some poimt in time to accommodate a short shaft motor on a long shaft boat. The fix is easy, first remove the steering cable fron the side of the transom and plug the hole. Then replact the wood without the drop cut and make it go straight accross then drill a hole in the crossmember and cap piece so it comes out at the same height as the top of the transom and you will be back to normal.
 

Groo

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Jul 31, 2017
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Make sure it does not flex at all if aluminium and consider the rest of the structure. Plywood flexes easily, but aluminum will Crack fatigue if flexed at all. The flex of the Plywood will take some of the shock that will be passed on down the line with an aluminum plate there instead.
 

icwingman

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Aug 21, 2017
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61
replace it what it came with dont do the cut out so you could raise your motor if needed
 
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