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Old 14 April 2011, 13:16   #1
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SIB Transom Strengtheners

Hi All,

Went on my first trip of 2011 last sunday and wow what a lovely day it was.

My 3.3m SIB is rated for a 15HP but i use a 25HP (QUE THE BOLLOCKING).

The transom was fine and did'nt flex much and boy did it go.

Just to be on the safe side i have installed some homemade transom strengteners and would like to share the idea with the forum for the benifit of others.

Made using M10 turnbuckles, o-clamps rivited to ali floor, dee rings and through-bolted to the transom and a large marine ply backing for more surface area.

Hope you like, Cheers.
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Old 14 April 2011, 14:36   #2
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I think with the turnbuckles the transom is only strengthened when the boat is stationary
when power is applied they will in effect be loosened off by the power of the motor pushing the top of the transom
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Old 14 April 2011, 17:23   #3
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I think the power of the outboard will move the top of the transom towards the rear of the boat, maintaining the tension, at least in forwards gear? I'm not an expert on transom braces but would something with no movement not be a better idea, possibly something triangulated?

Adam
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Old 14 April 2011, 19:34   #4
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Quote:
Originally Posted by theboysmiffy View Post
I think the power of the outboard will move the top of the transom towards the rear of the boat, maintaining the tension, at least in forwards gear? I'm not an expert on transom braces but would something with no movement not be a better idea, possibly something triangulated?

Adam

I'd agreed with that. If the transom really needs the bracing, the brackets should keep the transom at the angle the boat was designed to have it at, and prevent rotational movement in either direction. If such bracing is used, the floorboards might also need to be beefed up so they don't crack just ahead of the foremost part of the bracket.

The stringers might also need to be beefed up as well to handle the extra bending moment that would be applied at the joints between the floorboards (particularly the rearmost joint). Anytime you make one area more rigid, the energy that might have been absorbed at that spot will be transmitted further along the chain.
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Old 14 April 2011, 21:03   #5
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that thing definitely flies. have you checked your top speed via gps??
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Old 15 April 2011, 01:58   #6
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The turnbuckles are designed as per Adams theory. Like i said the engine is ok without the turnbuckles but there are just to stop the initial pull on the transom when accelerating up to the plain.

I have not yet recorded the speed but hope to soon and will keep you posted.

Cheers
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Old 15 April 2011, 09:05   #7
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Quote:
Originally Posted by weehaggisuk View Post
I think with the turnbuckles the transom is only strengthened when the boat is stationary
when power is applied they will in effect be loosened off by the power of the motor pushing the top of the transom

I think you'll find the force is rotational, pulling at the top and pushing at the bottom, the prop is at the bottom of a long lever, below the boat. if the prop was at top then yes you would get the effect you describe.

On a more practical note, ive had to beef up the transom of the jeaneau orange plastic tubs, and I can tell you the damage was a tearing at the top of the transom. I used a stainless version of this set up and it worked a treat, keeping the boats seaworthy for many years after the initial tear was seen
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Old 15 April 2011, 10:46   #8
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transom stiffener

You should definitely make sure you are at optimal pressure in the tubes. I had a customer who bent the bent and cracked an aluminum floorboard that the turnbuckle(factory installed) was connected to. Turns out he was not inflating the boat to proper pressure so the complete load was on the turnbuckles. The turnbuckle also bent. it was an expensive lesson for him as many manufacturers only sell complete floor sets. Hate to see it happen to someone else.
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Old 16 April 2011, 04:12   #9
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[QUOTE=Starovich;396794] I think you'll find the force is rotational, pulling at the top and pushing at the bottom, the prop is at the bottom of a long lever, below the boat.

I can see that now I sit at a keyboard corrected lol
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Old 18 April 2011, 03:39   #10
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It looks well engineered from the photo, well done....

What is the aluminium looking tube for that is fitted to the transom, I can see both sides of the transom?? An 'A' frame base???
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Old 18 April 2011, 10:50   #11
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Quote:
Originally Posted by simsy View Post
What is the aluminium looking tube for that is fitted to the transom, I can see both sides of the transom?? An 'A' frame base???
I thought it was the A-frame itself. Or at least the bottom of it...

jky
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Old 18 April 2011, 11:50   #12
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Quote:
Originally Posted by simsy View Post
It looks well engineered from the photo, well done....

What is the aluminium looking tube for that is fitted to the transom, I can see both sides of the transom?? An 'A' frame base???
Yes that is a light A Frame made from Ali tubing and stainless steel, holds the ensign flag, horse shoe buoy and cables for fishfinder.

Fishfinders a Humminbird piranhamax 160, excellent bit of kit, used it yesterday and caught more than ever before.
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Old 06 June 2011, 23:22   #13
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Finally

I knew I'd read/see this somewhere! Spent weeks sifting youtube and google...

Anyways I'm up to the same hijinks... I'll cut n paste from my local forum.

Hey guys

I'm looking at strengthening my transorm on my sib, but not too sure about the forces. I've drawn a diagram as to how I understand the forces, effects and possible solution but who knows if I'm right.

Blue = Boat and motor
Red = Forces
Green = Tension cables to possibly help take pressure off transom

I'm also considering right angle brackets, 4-6mm alloy sheet added to transom and extra pvc over rubber transom mounts.

For a change google was of no help!

I guess my current problem is an addiction to horses...

Boats rated to 15 and thats a 25 2st on the back. The boat handles very very well with that on the back, but I have figured I'm not using the boat for it's intended purpose/design (and plan to tow a tube/kneeboard!). So essentially I'm trying to decrease the negative effects of my actions and keep myself alive and afloat.

Good point on the flooring. Brackets are definitely being considered, just trying to get my head around a quick release but effective solution and keeping the boat portable.Using a few of these ideas may be better than just one solution maybe.



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