Water gushing up the sides of outboard

[JoeF1974]

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

Spray / Gushing water from Yamaha 30D - YouTube

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

[boristhebold]

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.

[ashbypower]

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.
Keron where are you when needed??

[CJL]

Too low!!!

[Sea Witch]

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

[Jorgos]

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 .

[captnjack]

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.

[Sea Witch]

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

[Sea Witch]

My 40v - now 50hp yamaha

[Sea Witch]

Originally Posted by Sea Witch

My 40v - now 50hp yamaha

If ur wondering wats d XF on d hood means Xtra Fast 40

[JoeF1974]

Originally Posted by boristhebold

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.

Wow - thank you for all the responses so far. Much appreciated!

The boat isn't stored at home, but I took a couple of photos of the outboard when I got it which I have just put up at https://picasaweb.google.com/1043743...42706542699698.

Not a stupid question at all as it does look a bit weird, but I am pretty sure that the lump of metal is supposed to be there. Will have a look in the instruction manual tomorrow to make sure I haven't made a real schoolboy error.

I would tend to agree that it looks as though it is too low, but the cavitation plate is pretty much skimming the surface of the water once on the plane (which I thought was about right) and it definitely goes a lot better with the motor sitting straight on the transom and it cavitates (I think? - you can feel the power slipping but the revs surge) a LOT more when I lifted the motor. Any higher and I think it will lose all power and barely move.

If I did lift it to stop the spray problem, are there propellors which would cope better with being at the surface of the water? There is plenty of water coming out of the cooling system, so I think it can handle being higher, but the lack of power and constant cavitation was frustrating.

There is also the slight problem of the clamps being off the top of the transom if it goes much higher. I want to bolt the motor on, but only once I am confident that the height is right. When I use the decking plank, I was really worried about the clamps popping off as they were very high.

Any other theories?

Thanks again to everyone - I am really grateful.

[Sea Witch]

R u racing urs or leisure use . Ur picture is showing an aluminum prop on , u need to get ur hands on a ss prop wit good cups on it pre 15 pitch for chop/flat or 13 pitch if ur out in the surf . Aluminum prop don't grip dat well at speed in d corners on cats.ie zapcat , ceaser , aqarius or Gemini hulls .

[captnjack]

Your picasa album doesn't work for me here in the States.
But in your video, near the beginning where you say "raised 1.5cm" the outboard is still too low there. The metal blobby bits are supposed to be on your lower unit, the whole thing is just still too low.

I would guess your 30hp did not come with the correct prop to run that cat really fast. That's why it ventilating (drawing too much air in from the surface). As Sea witch says you need a cupped prop which may be hard to find in smaller sizes for a 30hp.

[JoeF1974]

Originally Posted by captnjack

Your picasa album doesn't work for me here in the States.
But in your video, near the beginning where you say "raised 1.5cm" the outboard is still too low there. The metal blobby bits are supposed to be on your lower unit, the whole thing is just still too low.

I would guess your 30hp did not come with the correct prop to run that cat really fast. That's why it ventilating (drawing too much air in from the surface). As Sea witch says you need a cupped prop which may be hard to find in smaller sizes for a 30hp.

Sorry - I did check the link but think it worked as I was logged in. I think https://plus.google.com/u/0/photos/1...42703085227489 should work?

I think you are right that the propellor is not working for the boat. I have no idea what a 'cupped prop' really means but will have a search and see what I can find out. I have come across various phrases such as cleaver / chopper / bunny, all of which mean next to nothing to me but I am sure the answers are out there.

Thanks again for the help. If anyone has any views on how to source a new prop, then I am all ears.

Cheers,
Joe

[JoeF1974]

Hmmm - not as easy as I had hoped, although I have got my head round the various types of propeller available.

Any advice / thoughts on where to source decent SS props in the UK?

Thanks
Joe

[sinner]

I would suggest that you leave the motor height as you have it for best performance. Now you still have the water gushing problems. So..., fabricate a "water spray shield" out of pieces of pvc material, or aluminum plate, or whatever to attach on the transom on either side of the motor to deflect the majority of water back. The would be triangular in shape. If you make it out of pvc fabric it could attach partially with snaps to be folded back to facilitate in removing/attaching the motor.

Some sib's are made with these shields from the manufacturer.

The problem is your boat rides so high on the water when on plane that to raise it up to prevent the slow speed water-gushing problem you have cavitation issues, as you found out.

This would be cheaper than buying new props to experience with, if that is an issue. Otherwise, raising the engine and trying different props will probably fix the issue rather than just fixing the symptom.

[captnjack]

Ok that link worked. Maybe a dumb question but is that the correct shaft length for the boat? Looks like it might be 20inches. Aka a long shaft

[JoeF1974]

Hi Sinner,

Thanks for the advice. I have seen a few splash guards on similar boats, so had thought about that.

I do, however, like your comment:

Originally Posted by sinner

Otherwise, raising the engine and trying different props will probably fix the issue rather than just fixing the symptom.

In the ideal world, it would be good to get the height right and still have the performance.

Thinking about it more today, the boat is a lot lighter to drive and easier to steer with the motor a bit higher. Whilst it is incredibly direct when at the lowest setting, it somehow feels a bit too grippy and there must be a lot more drag. You certainly feel it on your arm and the boat was veering off to the right a bit. I think you could fix that with the little tab, but I am tempted to try a different prop to see if that can achieve a magical balance.

I don't mind getting a bit wet and am still loving it but am now addicted to getting the most out of it in terms of speed. Will sink a bit of money into right prop if that will help.

Thanks again,
Joe

[JoeF1974]

Originally Posted by captnjack

Ok that link worked. Maybe a dumb question but is that the correct shaft length for the boat? Looks like it might be 20inches. Aka a long shaft

Not a dumb question at all but I am 99.9% sure that it is a short shaft as all the documentation says that it is and it was sold as a short shaft (I got it 2nd hand, albeit hardly used).

The manual is in my car so am going to double check this evening and have a look for the propellor specification, but I may go and physically measure it to make sure tomorrow (boat stored about 15mins from work).

Thanks
Joe

[Sea Witch]

Dis wat there used for !!!!!