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Old 16 November 2011, 12:33   #1
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Water gushing up the sides of outboard

Hello everyone - please beware that I am a 'noob' and have only recently got a boat, so sorry if this is a day 1 question...

In a nutshell, I am convinced that the amount of water gushing up the side of my outboard can't be right - I have tried messing around with engine height but am not convinced that is the route of the problem.

A bit of background - the boat is an oversized zapcat style boat (bought from Howy via this forum, thank you forum and thank you Howy!) with a 30hp yamaha 3 cylinder engine. The boat can handle up to 50hp, but I foolishly thought that I wouldn't want anything too wild. Already want a 50hp for it as it is more fun than I thought possible. :-)

I have now been out 4 times, as follows:

Trip 1:
-2 on board
-a LOT of water gushing up the side of engine and swamping the back of the boat (it drains out, but there was a lot there)
-being a bit tentative on first trip so didn't realise that the problem went away if you opened it up and went for it.
-once fully on the plane, the boat is superb. Quick but rock steady. Lots of grip from the propellor and lots of fun until you slow down, when niagra falls makes an entrance over the back of the transom
-we tried every trim setting and the problem was there each time. Fastest setting was 3 holes up from vertical.

Trip 2:
-2 on board
-I was convinced that the engine needed lifting as the spray goes away once you are on the plane, so I lifted it using an offcut piece of decking plank. I can't remember the exact lift, but it was quite a bit (over 4cm)
-MUCH improved spray situation but the boat felt slower and the propellor was slipping / cavitating (not sure of exact term but the revs would shoot up and all bite was lost)
-GPS gadget was reporting max speed of 28kph until my passenger got out (to be sick! Hangover / wetsuit tight around his neck / sea sickness problem...) and I got it up to 44kph on my own, but felt a bit flighty

Trip 3:
-2 on board
-having decided that it was too high, but along the right track, I dropped the heigh a bit to just under 2cm.
-a bit more spray than before and still quite a bit of cavitation
-GPS reported 49kph and it was quite rough

Trip 4 (today):
-1 on board
-decided to leave the height to see if the difference in weight would make a difference
-still quite a bit of spray and cavitation. Topped out at 44kph despite being pretty flat
-I stopped and got rid of the stips of wood that I was using to lift it and immediately noticed a marked increase in grip and speed. It did cavitate a little bit on occasion but not nearly as much and it was faster (56kph). Just felt better allround but the spray was worse again.

I am now torn - the water gushing problem is reduced if you lift the engine but it definitely doesn't help performance.

The propellor is the standard 3 blade job that comes with the engine. Would a different propellor allow you to run the engine a bit higher?

I took the camera out today and there is a dodgy edit at which I hope helps to show the problem as it is hard to really explain. The video has two heights of engine, but you can hopefully see the issue.

Am I being mad and that is perfectly normal or is there something not quite right? Whilst you can get over it be flooring it and jumping up on the plane, it seems odd that you can't cruise without being drenched?

Any thougts or pearls of wisdom would be very welcome. I am loving the boat and it is a blast, but I just can't help think that there must be a solution to the water gushing up. I have got over my fear of it actually swamping the engine, but would rather it wasn't so bad.

Many thanks for any help,
Joe
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Old 16 November 2011, 12:59   #2
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It looks very odd, maybe a stupid question but there isn't some form of hardware still attached that should be used only when the boat and engine is being towed by a car? Something about the lower leg looks strange as in what is that big hunk of metal attached. Lower legs should be streamlined but yours looks the opposite and that appears to be where the water is shooting up from. Perhaps you could take a pic with the engine raised while out of the water so we can see lower leg.
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Old 16 November 2011, 13:38   #3
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Know nothing about Zapcat type setup's but could well be a shaft length issue. What shaft is the OB ???
Ribshop on here is yer man.
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Old 16 November 2011, 16:45   #4
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Too low!!!
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Old 16 November 2011, 16:53   #5
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I have a zapcat and dat normal at slow speed - high jackers should b 10 psi and sponsons should b 4 psi . I have 50 hp yamaha have it up one hole up on transom hitting 50 mph
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Old 16 November 2011, 17:14   #6
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I read somewhere that the propeler if is made more sharp ( lets say like razor) the water is much less. They say the outboards are designed for single hull boats and not for cats.

Also if you see on that photo


there is an inox extension on just on the front of the motor . that helps for less water .
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Old 16 November 2011, 17:28   #7
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The outboard is too low. Raise it up until the cativation plate is even with the bottom of the hull. Then possibly lower the trim pin.
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Old 16 November 2011, 18:05   #8
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Guys it's a zapcat , wen cat going 50 mph it's skating across the top of the water , only thing in the water is gearbox , not like a rib dat cavitation plate needs to b level with hull
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Old 16 November 2011, 18:11   #9
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My 40v - now 50hp yamaha
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Old 16 November 2011, 18:27   #10
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Quote:
Originally Posted by Sea Witch

My 40v - now 50hp yamaha
If ur wondering wats d XF on d hood means Xtra Fast 40
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