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Old 06 March 2018, 03:51   #11
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>>>Thundercats definately run short shafts check the specs

Yep my thought while I chomped my toast this morning. Folks tend to take dramatic pics of them catching air and it's quite hard to find one running fairly normally to demonstrate how the design works Lee. But the one I've attached below shows fairly well that in normal running their central "deck" the transom is on plays no part in contacting the water hence the cav plate relationship to the deck is nothing to do with getting the prop in the right place or best shaft length.

>>> SIB power boaters who want to thundercat

You can't Thundercat a SIB... different beasts completely.
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Old 06 March 2018, 06:50   #12
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Definitely short shafts on thundercats...
If you try a long shaft you either have the engine 5" too deep in the water and the boat will handle terribly and be slow with too much drag, or if you run the engine 5" up on the transom you'll have an excessively high centre of gravity and potentially roll the boat during high speed turns.

The cavitation plate is roughly in line with the bottom of the hijackers on a thundercat
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Old 06 March 2018, 12:30   #13
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I tried my long shaft on a suzimar sib and I thought the transom was going to fold into the water if you went near the throttle. I figured it was due to the engine but maybe wasn't enough pressure??....too late to find out as the sib went ages ago.
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Old 06 March 2018, 17:25   #14
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Quote:
Originally Posted by Lee1 View Post
, my post was how I keep the prop in the water planning or wave jumping at 30+knots by having the extra 5 inches length of a long shaft over a short shaft.
Iím sure you appreciate/the extra 5Ē but I think you kind of missed the point of wave jumping there..... drop 300 horses in a 3m hull and a negative shaft length and try wave jumping pushing 50knts and youíll know what I mean......

Having fun and going fast arenít the same, maximum thrust & minimal drag doesnít make for exciting pictures.....
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Old 07 July 2018, 13:09   #15
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Originally Posted by HDAV View Post
Iím sure you appreciate/the extra 5Ē but I think you kind of missed the point of wave jumping there..... drop 300 horses in a 3m hull and a negative shaft length and try wave jumping pushing 50knts and youíll know what I mean......

Having fun and going fast arenít the same, maximum thrust & minimal drag doesnít make for exciting pictures.....
I assume you have tried a sharp turn with a longshaft engine on a shortshaft transom?

Aa while ago i dropped my rib aux onto a borrowed dinghy... it was either that or stay ashore. Aux is longshaft, dinghy was short. Even with only 5hp on a 3.1m sib and being carefully experimental I nearly had it upside down numerous times on the corners...

And the drag was horrendous - the engine was labouring the whole time.

But if you have a grunty engine & want to play in the waves go for it!
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Old 07 July 2018, 16:55   #16
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Iíve tried too long shaft on my sib (Zodiac FC 470). The engine was tuned Yamaha giving 40-50 HP. There was no major benefit with a too long shaft IMO. Even at top speed and rough waves.

The major disadvantage was the splashing into the sib and higher fuel consumption. The splashing was hopless when travling long distanse.

Cheers
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