HELP, New Prop is Causing Splashing!...

[HughN]

Originally Posted by J@mes

...I have noticed before that in dead calm seas my max speed is a couple of mph less than when there is a bit of chop/waves.

The chop lets some air get under the boat more easily than in a dead calm sea and reduces the amount of hull in contact with the water = less drag.

[sparky666]

Once on the plane trim the engine out until the bow starts to porpoise ( bounce up and down) then trim in slightly until you get a stable ride , don't get hung up on what the engine looks like , go by the feel
What's your top speed?

[breghall]

Originally Posted by J@mes

Also today I checked the engine height on the transom, the water deflector plate is above the bottom of the keel, its about the same height as the top of the water outlet bung in the transom. Also the anti cav plate is virtually level with the bottom of the tansom/hull, so I am 100% sure my motor height is fine. Like I said the motor was mounted to the rib at the Tohatsu UK headquarters, so they should get it right!!

Also I managed to take some pictures whilst we were cruising at about 3000 - 3500 rpm (3 up in the boat)...

http://i24.photobucket.com/albums/c2...0-15163812.jpg

http://i24.photobucket.com/albums/c2...0-15163822.jpg

http://i24.photobucket.com/albums/c2...0-15163835.jpg

http://i24.photobucket.com/albums/c2...0-15163844.jpg

and finally...




How do the pictures look to everyone? (the extra splash in the pic above on the left hand side is because I am sitting right at the rear on that tube!)

Your engine is too low in the water when under way, you should clearly be able to see your anti-cav plate when travelling. Try move some weight up to the bow or else raise your engine up by another hole or two. It may have been set up by the dealer but did they give it a test run on the water?? every craft has their own optimal set up.

[biffer]

I thought I'd better post before you get bogged down with advice, your old prop never did it but the new one does, what does that tell you, if your engine was too high or low the chance are your old one would have shown some tendency s to do the same as the new one, there are a number of ways to squeeze a bit more out of props, buying one off the shelf is always a comprise, cupping feathering repitching is a dark art and best left to a professional, my advice for what it's worth is look at what the boat is used for most, ie people on board, kit etc and get the prop sorted for that and then leave it alone

[J@mes]

Originally Posted by sparky666

Once on the plane trim the engine out until the bow starts to porpoise ( bounce up and down) then trim in slightly until you get a stable ride , don't get hung up on what the engine looks like , go by the feel
What's your top speed?

Ok cheers for that. WOT on my own is 62kph (38.53mph).

Originally Posted by breghall

Your engine is too low in the water when under way, you should clearly be able to see your anti-cav plate when travelling. Try move some weight up to the bow or else raise your engine up by another hole or two. It may have been set up by the dealer but did they give it a test run on the water?? every craft has their own optimal set up.

Don't forget in those pictures my engine is fully trimmed in and I am sat right at the rear of the boat where no one ever sits which will obviously not help the pictures! Lastly I double checked the height of the motor and it is in accordance with the Tohatsu mounting instructions.

Originally Posted by biffer

I thought I'd better post before you get bogged down with advice, your old prop never did it but the new one does, what does that tell you, if your engine was too high or low the chance are your old one would have shown some tendency s to do the same as the new one, there are a number of ways to squeeze a bit more out of props, buying one off the shelf is always a comprise, cupping feathering repitching is a dark art and best left to a professional, my advice for what it's worth is look at what the boat is used for most, ie people on board, kit etc and get the prop sorted for that and then leave it alone

This is exactly what I am doing. I am back on the OEM 11.1 x 13 prop as it is fine for everything except when I am on my own at WOT where it hits the limiter just, so I will have to back off ever so slightly and not go WOT on my own, a small compromise I guess.

[PeterM]

I think you're getting as much as you can out of the rig...irrespective of prop changes it won't go much quicker.

[jyasaki]

Originally Posted by J@mes

Lastly I double checked the height of the motor and it is in accordance with the Tohatsu mounting instructions.

That's generally a starting point for mounting the motor. Usually a bit of trial and error is involved to fine tune the setup.

I am back on the OEM 11.1 x 13 prop as it is fine for everything except when I am on my own at WOT where it hits the limiter just, so I will have to back off ever so slightly and not go WOT on my own, a small compromise I guess.

That actually sounds about right to me. Runs well when 1 up, and still has a bit of oomph when you're with company.

jky

[SIBRider]

I doubt you can fined 13.5 prop. But 14 might be fairly safe bet. Should push you to about 40 mph with you alone without over-revving engine. Keep eye on that trim. If you been running as in picture one with engine trimmed-in that would rob you for some power too forcing your bow down. Pic #2 looks much better but I would experiment as you go to find best settings.
Are prop's so expensive on other side of pond? Over here 14” Pitch Tohatsu Outboard Boat Propellers 50 HP 1992 & Newer Except 50C, Includes TLDI - iboats it's what, cost of gas for 1 good outing?

[J@mes]

Originally Posted by PeterM

I think you're getting as much as you can out of the rig...irrespective of prop changes it won't go much quicker.

Originally Posted by jyasaki

...That actually sounds about right to me. Runs well when 1 up, and still has a bit of oomph when you're with company...

You are indeed correct, and according to this Prop Slip Calculator 15p@5000rpm is 39mph, 14p@5500rpm is also 39mph and 13.5p@5750rpm is 40mph as is 13p@6000rpm so in other words speed wise I wont really get any more out of it! But I was not looking to change my prop for speed, that was a bonus, I just wanted to stop WOT with just me in the boat to not be above 5850rpm! I will just have to back off ever so slightly once I have gone to WOT when it is just me in the boat! This way when 2 or 3 up in the boat WOT rpm will be very good/healthy.

Originally Posted by SIBRider

I doubt you can fined 13.5 prop. But 14 might be fairly safe bet. Should push you to about 40 mph with you alone without over-revving engine. Keep eye on that trim. If you been running as in picture one with engine trimmed-in that would rob you for some power too forcing your bow down. Pic #2 looks much better but I would experiment as you go to find best settings.
Are prop's so expensive on other side of pond? Over here 14” Pitch Tohatsu Outboard Boat Propellers 50 HP 1992 & Newer Except 50C, Includes TLDI - iboats it's what, cost of gas for 1 good outing?

I have found a 11 1/8 x 13.5 prop. Props here are indeed that much more than over the pond! =( My solas cost me £105 delivered and that was the best price I could find! As for speed that is a good point re my trim. All max speeds I have ever done have always been with the engine fully trimmed in. Next time I will try with it trimmed out a little bit, would be nice if my gps speedo went from 39mph (really its 38.53mph! (62kph)) to 40mph haha but I doubt it!!

[J@mes]

Originally Posted by PeterM

I think you're getting as much as you can out of the rig...irrespective of prop changes it won't go much quicker.

Out of interest what speed does your 4m Avon with 50 yam achieve?