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Old 04 July 2012, 15:51   #1
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Spray from tohatsu 50 above cav plate

Diificult title sorry ,
Have recently changed boats and was forced to convert my Beloved tohatsu 50 from short to long shaft . Expensive but all has worked very well so worth it.
The long mid section has a (small cav plate / fin ) don't know what its called but above the cav plate is a another smaller cav plate /fin on the short shaft and the long shaft has 2 of these as there is one on the new mid section casting .

Anyway the second / top plate / fin is causing an anoying spray up the transom that is constantly soaking the rear tubes . Its more anoying than a problem but if its windy it can add to the spray

I am tempted to grind the dam thing off as it seems to serv no purpose its a drastic step . any ideas anyone have a tohatsu 50 long shaft that does the same

The motor is set right, height and trim etc and the boat is performing very well indeed .
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Old 04 July 2012, 17:05   #2
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At speed, on plane, the main anti-ventilation plate (the one just above the prop) should be at the water's surface, or just below. Some say it should be clear of the water, as long as no ventilation occurs. Sounds to me like the engine is sitting too deep.

jky
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Old 04 July 2012, 17:15   #3
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I know what you mean . The engine height is correct thats not the problem , the top plate thats causing the spray is above the water level , its just the water is sort of deflected off it which is causing the spray .
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Old 04 July 2012, 17:21   #4
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Might sound stupid but could you fit hydrofoils to deflect it?
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Old 04 July 2012, 19:48   #5
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if you mean those plastic whale tail things they call doel fins or something like that . NO WAY
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Old 04 July 2012, 20:03   #6
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OK, stick some other sh.te on it to stop it
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Old 04 July 2012, 20:07   #7
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Old 04 July 2012, 21:14   #8
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Engine sounds to deep in the water if its kicking up spray.
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Old 04 July 2012, 22:05   #9
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Quote:
Originally Posted by Turbodiesel View Post
Engine sounds to deep in the water if its kicking up spray.
Hi Rob

Iam sure its at the right height , i think its the just the way the keel ends and sends a jet of water against the upper plate . Its hard to take a good look while iam driving the boat and i can't find any calm water at present

May be best if i launch at looe one day soon and get you to come and take a look . I was going to get you to check the tune of the motor sometime anyway .
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Old 05 July 2012, 12:31   #10
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I wonder if what you are seeing is water being forvced up the front of the leg whioch if that plate wasn't there would jetwash your "rudder bearing" nicely.

If it is simply upward moving water bouncing off the plate, could you bend it down a bit at the outer edge to deflect the water back down rather than out sideways? A bead of sikaflex might have the same effect?


Somewhere out here I posted a pic I got of my cav plate at speed (got a friend to drive at a steady speed, tied the (waterproof) camera to my wrist and I hung on to the A- frame and went "click - click - click ...." through the spray at what felt like slightly differnet angles.

I got 25 odd photos - three showed me what I needed to know. The rest were at best "artistic".....
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Old 05 July 2012, 15:01   #11
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[QUOTE=9D280;473327]I wonder if what you are seeing is water being forvced up the front of the leg whioch if that plate wasn't there would jetwash your "rudder bearing" nicely.

If it is simply upward moving water bouncing off the plate, could you bend it down a bit at the outer edge to deflect the water back down rather than out sideways? A bead of sikaflex might have the same effect?


Thats exactly what appears to be happening , you have described what i was having trouble describing Thanks .
The old short shaft didn't have that 3rd plate , but as you say if its protecting the steering bearings then i will live with it . However it is soaking the underside of the motor which never used to happen .
I suspect that if it was used on a boat with power trim then the it would probably become streamlined when trimmed for cruising .
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Old 06 July 2012, 15:14   #12
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In that case if you do a lot of cruising, it is worth living with a slightly more sluggish time to plane by lifiting it out a pin or two?

When I had an SR4 / Suz 25 I used two trim positions - one was for cruising, and then I would drop it a hole if I was being rescue boat. The cruise position I had to live with an aeon to plane, but once there it handled perfectly.
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Old 06 July 2012, 17:09   #13
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if i was cruising a long way then i would lift it a hole , it does reduce the spray a little . it only gives about 1-2 mph more top end but it will ventilate too easily if you turn a bit quick. we are in and out of surf a lot so don't want it slipping because i forgot to drop a hole .
Its never sluggish the boat only wieghs 105kg and comes out faster than you can twist the throttle
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