Anybody changed from a 3 blade to 4 blade prop?

[GLXMAN]

Just wondering what your experience has been,
Worth changing from the standard or marketing BS?

My Allison 4.95 plate alloy really scoots along in calm water, achieve top revs OK
but with 2 up and a bit of weight on board, stern bogs down at around 10knots when the sea breeze kicks in,
I can get it out of there OK but then I'm too quick for the sea conditions

FWIW, I have a 60hp 4s Merc 1012 (i think)
Your thoughts!
.......Gary

[tunaticer]

Running the diameter and pitch 4 blade increases the load on the motor.
More load = less effective holeshot.
Reducing the pitch and or diameter will decrease load on the motor, decrease top end and should improve holeshot.
There is a point in reducing diameter and pitch will peak for best performance then die quickly with further decreases.

There is no formula to work out which is best for your boat......purely trial and error from a known starting point.

I suggest drop your pitch 1/2" or maybe 1" on a three blade and see what happens.

[Feral]

Ray has gone form a 3 blade to a 4, much easier to get it on the plane. In fact he stuffed the 4 blade first day at the Maroon dam comp and we had to go back to the 3 blade. For the second day, boat wouldn't plane with the 3 blade with the 60litre shrimp esky filled up once the day warmed up. (Only just got there in the cool air early morning). Ploughed around the dam at 14kph all day.

[GLXMAN]

Very positive, tks for the feedback
much appreciated,
might just for an alloy first until I get it sorted
......Gary

[Crocodile]

Hello GLXMAN,

My reading of your question is that you want the boat to plane at 10 knots for comfort in choppy seas.
Very few boats plane cleanly at that low speed.
It may not be a propeller issue at all.
Have you tried weight shift forward?
Have you tried a foil?

[DATCOL]

GARY Solas Stainless 4 blade is the best improvement ever on my Gullwing, Better in all sea conditions & better economy, I did take it back to solas & they cupped it for me Works great
Tried a foil & made it worse Cheers COL

[scottar]

Whilst a 4 blade will help, the single biggest difference will be made with either a foil or trim tabs in relation to achieving a slower planning speed. All hull/motor combinations are different so unfortunately finding the best solution for you is a matter of trial and error that can be somewhat expensive. I have been playing with my current rig on and off for the last two years trying to achieve better economy with my current rig at lower planning speeds with the final result being achieved via a 4 blade prop, lifting the engine and a set of trim tabs. On the way to this result I have also tried two other 4 bladers and two different foils. On my previous boat, the same result was achieved with the addition of a foil alone. If I had to pick a single item after this process that made the biggest difference it would be the trim tabs.

[GLXMAN]

Tks guys,
Appears a 4 blade from Solas might do the trick
I've played around with weight, its not far off, just a little extra may just do it
..........Gary

[gofishin]

Whilst a 4 blade will help, the single biggest difference will be made with either a foil or trim tabs in relation to achieving a slower planning speed. All hull/motor combinations are different so unfortunately finding the best solution for you is a matter of trial and error that can be somewhat expensive. I have been playing with my current rig on and off for the last two years trying to achieve better economy with my current rig at lower planning speeds with the final result being achieved via a 4 blade prop, lifting the engine and a set of trim tabs. On the way to this result I have also tried two other 4 bladers and two different foils. On my previous boat, the same result was achieved with the addition of a foil alone. If I had to pick a single item after this process that made the biggest difference it would be the trim tabs.

Gary, scottar's post above is great advice and covers the setup 'holy grail' items of optimising low speed planing performance in any planing hull.

I would like to add; with tin boats there is often greater scope for raising the donk than with glass boats - which can have a considerable 'positive' impact on low speed planing performance.

Although it may have been sold as a 'plate boat'(flat side sheets?), I suspect it may have the main attributes of pressed construction, including an I-beam keel extrusion, with the external keel extending right to the transom. (Note, guessing here, don't know Allison tin boats at all).

If so, you also have the option of a keel-cut, which will allow you to raise the donk one ore two holes higher again, depending on the prop.

In the good old days, all/most would have this done when they are built. Nowadays, time is money, and with everyone chasing the last few dollars in a deal manufacturers stopped this practice some time ago.

Do a search on here and you should find some info and even pics etc.
cheers
Brendon


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[GLXMAN]

Tks Brendon
Yes did think about raising the motor but I think the cavitation plate is about right
I'm hoping an alloy prop from Solas will be enough, and if it works, I'll eventually get a SS one
........Gary

[Kero]

Have you looked at these? Mercury Spitfire.

http://www.mercurymarine.com.au/medi..._flyer_fa3.pdf

[Noelm]

Alison is a true plate boat, it is not pressed.

[GLXMAN]

Have you looked at these? Mercury Spitfire.

http://www.mercurymarine.com.au/medi..._flyer_fa3.pdf

Yes, have checked them out, going to price them up on Monday
........Gary

[GLXMAN]

Alison is a true plate boat, it is not pressed.

Yes, love the boat actually, pity they are not with us any more
......Gary

[gofishin]

Alison is a true plate boat, it is not pressed.

Well there you go, will have to check one out some day.



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