Chosing correct propeller pitch for outboard (zodiac)

[nathan007]

Hello everybody!

This is my first post on this forum and i was curious about recommendation for a new propeller.

I run a 2008 Yamaha F15 four stroke, mated to a new 11' Zodiac Caribe RIB, which is alot heavier than the previous zodiac 10' with plywood floor.
I just added a hydrofoil and it's easier to get on a plane but i still find it underpowered. I know the propeller need to be changed since it's been slightly damaged and causes undesired vibration. Current pitch is 11 on a 9.25 prop. i did a test run with 3/4 full tank of gaz (20 liters capacity), normally loaded zodiac with only me aboard and was running 5400 rpm (unknown speed)

Now i would like to make it abit faster, but reality is most of the time water is too choppy to go fast safely. Getting on a plane faster and remaining there with less power would be fine. Half the time i'm alone, other half i'm carrying 2 adult passengers for an extra 300 pounds.

Should i go one pitch size down or keep my current setting but with a new, good working propeller?

Thank you!

[tuffr2]

Since you need a new prop anyway i would move down 1 degree in pitch of possible. I know the props I deal with usually go up/down in 2 degree increments. But it has been a while since I was in the prop market.

I say reduce pitch because you are pushing a heavier boat.

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[nathan007]

Thanks for your reply tuffr2, I was looking at solas amita 3 which makes it in 11 and 10 pitch, keeping it a 3 blade. So I would bump the revs up but still in the safe zone

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[tuffr2]

I googled your motor to double check what the engine max revs are. I show the WOT rpm range to be 5,500 - 6,000. I still think you should reduce from a 11 pitch to a 10 pitch.

In my language the 11 degree pitch would be the 'speed prop' and 10 degree pitch would be the 'power prop'.

I played around with a 21 degree pitch vs a 19 degree pitch (same diameter 3 blade).

If I was water sking I would use the 19 degree pitch. If I was out for crusing the lake I woukd use the 21 degree pitch.



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[Brewgyver]

Prop pitch is measured in inches per revolution, not degrees.

[tuffr2]

Agree...the word degree should be removed. Props are not measured in degrees ....just pitch...good catch.

Bottom line...you will notice just a slight increase in acceleration with a 10 pitch prop vs a 11 pitch prop. The 10 pitch prop will be better for the heavier boat.

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[nathan007]

Will try a 10 Pitch, i'll come back with an update next week!

[tuffr2]

Zoom zoom....

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[Lepke]

You might try a marine professional that sells propellers and has the experience of hundreds of boats, not just a bunch of people tell you about their boat.

[tuffr2]

You ever get that new prop? If so how is it working out?

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[nathan007]

Yes i did! I totally forgot about it haha

I first got a solas amita 3 with 10 pitch, it made my engine rev to 5800 and did not seem to like hauling extra weight, took forever ran it for the weekend and did not enjoy it.

Now i got a solas amita 4 (4 blade prop) with 10 pitch, that thing rocks. I did not get a chance to try it with extra weight of passengers, but it will get out of the hole in no time, plane wayyy slower (almost half throttle) and even go faster (36km/h vs 38.5km/h!) at 5400 rpm! I defilitely do not regret this purchase!

[a64pilot]

Interesting, four blade prop I had not considered one.
My Zuk came with a 10" pitch, would hit rev limiter very early but would jump onto plane with four adults, so I went with a Solas three blade SS 12" pitch, With one one board, thing is scary fast, will not hit rev limiter, but will not plane with four adults, struggles with three and even then everybody has to lean forward as it crawls onto plane, much less jump like it did with the 10" prop.
Went with an 11" Solas three blade SS prop, still way more pitch than the factory 10", I believe the cup on the SS props is more, meaning more effective pitch than just the number of inches indicate, meaning that the same pitch on a Solas SS prop is more pitch than the factory aluminum Zuk prop.

I had not considered a four blade, but I can see how it might be better, Bass boat guys run four blades and claim they get on plane faster and without as much bow rise that a three blade has.

[tuffr2]

Great...sorry I have no experience with anything but 3 blade props. I have heard 4 blade props have more 'bite'.

Now you are zoom zoom!!!

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[nathan007]

It would be more fun with a 25hp since the fiberglass hull really made the weight go up, but i'll try a few things before i dish out 4k (CAD) for it!!

Next step will be to try and raise the motor since it sits too low in the water (low transom, 20" shaft) but i doubt 1 1/4 inch will improve much (i will by no way drill holes into a brand new hull!! in order to raise it further, safely)

I would have liked a SS blade, but the cost and uncertainty of performance upgrade made me go aluminium.. I am really anxious to try it with 1 or 2 other adults in 2 weeks to see how it handles.. But solo it's never been better!

I'm learning some thing new everyday about this lol..

[clownfishsydney]

We have a 3.4 m RIB (11.25 feet) with 15 hp Mercury 2 stroke running a 9 inch 3 blade prop. This will plane with three reasonable sized people and some gear but not four. I purchased a 7 inch 3 blade prop in the anticipation that this would plane better. It did not, in fact it was worse, so I returned to the 9 inch prop. Not sure why it did not work, as theoretically it should have been a lot better.