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Old 21 May 2013, 17:54   #1
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tohatsu 18 engine depth

Hi iv just bought a 18 ho tohatsu long shaft to go on my old 12 ft zodiac sib..when the engine is on the boat the cavitation plate on the engine is about 6' lower than the bottom of the boat....its go hydra foils fitted...iv run it for a few miles today and its great..doesn't poor water into the boat and jumps fairly instantly onto the plane......iv easy access to a tig welder and aluminum...is it worth the effert of building a transom extension to lift the engine upto the correct height?? Will it make a lot of difference..speed handling??
Thanks in advance for any info...
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Old 21 May 2013, 19:04   #2
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What's your transom height in cm ? Do you have inmaculate flat water flow, or slight water splash splasing back transom ? My long shaft 18 gave excessive water shower out transom.

Check this to see if we are speaking same Tohatsu language.

Matching a long shaht engine to a medium size transom.

Happy Boating
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Old 21 May 2013, 20:03   #3
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From the bottom of the boat to the top of the transom is 16" or 40cm

The engine from the top of the engine mount were it sits on transom to cav plate is 55 cm 21 1/2"

I ran it today on perfectly flat narrow water ( bit like a canal). The water from the back of the boat wasn't splashing up like the pics in the link..
I'm goin to run the boat on rivers...7 and dee. And will be going in the sea.....
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Old 21 May 2013, 20:06   #4
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Old 21 May 2013, 20:12   #5
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Old 21 May 2013, 20:16   #6
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All as iv done is straight line stuff haven't a clue what its like in turns or deep water...its up on the plane within a couple of seconds with me steering 16 stone and my friend in the front 19 stone....I haven't run it without the hydro fins they are a real pain when trying to carry the motor to the boat on my own
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Old 22 May 2013, 04:57   #7
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woz,

The fins are a good debatable point! If you do a search here (try also "Doel fins") you wll find much heated debate on their pros & cons.....

One thing is certain - they give lift so will get you on the plane much quicker.

Down side if your engine is a long on a short shaft sized transom, those fins will create drag, as will the extra leg length. (Some peeps have posted pics / reports that their fins leave the water once on the plane - that certainly won't happen with excess leg length.) Might be worth trying without them. Worst case - you bolt them back on!

If it's running fine then maybe you don't need to raise it, BUT be aware that you have a lot more underwater, so be careful near beaches / shallow water etc!
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Old 22 May 2013, 07:42   #8
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And you also have 6 inches further to reach out should you need to clear the prop of plaggy bags or weed.
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Old 22 May 2013, 07:47   #9
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I'll fabricate a transom extension up and see if it makes any differece....I'll post some pics and let you know
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Old 22 May 2013, 09:08   #10
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Other thing to watch is weight.....

To raise an engine 6" I'm guessing a chunk or two of 1/2" ply might be involved.......
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