Prop Selection ?

[Kraftei]

I have a question for the propeller experts.  My Yamaha F250 came with a 19 M aluminum prop, I’m assuming it’s a Yamaha. I was planning to replace it with a stainless prop.

The first time I took the boat out I kept it under 2000 RPM for the first hour (to break the motor in) and then I accelerated coming back to the marina. I passed a boat and I picked up a mild chine walk, I thought it was from the waves. Today I picked up three cute hitchhikers and I wanted to show off so I accelerated. All three of them were sitting behind me so I possibly had too much weight to the rear. This time I had a bad chine walk, worst I’ve ever experienced, nearly tossed me. Massive bruised ego, a bit of a scare..

I eliminated most of the issues associated with chine walk. I’m left with too much weight to the rear (the passengers) the wrong prop and I possibly over trimmed.

I am hitting 57 mph at 5700 RPM. With the information that I’ve given, any recommendations for a prop? The boat is a zodiac pro seven,. Thanks !!

[paintman]

Is the size of the engine within the range given by the boat manufacturer?

Is the 5700rpm at Wide Open Throttle and is it within the manufacturer's WOT range for that engine?
And that figure is obtained with the boat/engine correctly trimmed & carrying its normal load?

If you change the load it will change the WOT rpm & it may need a change of prop to bring that back with the range.


If you corner too sharply & too fast then at some point it's likely the boat will start to skid sideways resulting in chine walk & hooking. That's driver error.
You might find this precis of the MAIB report into a double fatality at Padstow worth a read: http://www.mby.com/news/padstow-rib-...-released-1808

I'm inclined to think that your extra large load and its positioning made it that much worse when it did break away.

May also be that the speed & the lift ends up with so little of the hull in contact with the water that even in a straight line it can make the handling unpredictable & hitting a wake or wave could cause unexpected problems.
Being a cathedral hull dory I notice this on my own boat & it's a too fast for the conditions issue.

[Wave Rider]

Ask steel developments

[Kraftei]

Originally Posted by paintman

Is the size of the engine within the range given by the boat manufacturer?

Is the 5700rpm at Wide Open Throttle and is it within the manufacturer's WOT range for that engine?
And that figure is obtained with the boat/engine correctly trimmed & carrying its normal load?

If you change the load it will change the WOT rpm & it may need a change of prop to bring that back with the range.


If you corner too sharply & too fast then at some point it's likely the boat will start to skid sideways resulting in chine walk & hooking. That's driver error.
You might find this precis of the MAIB report into a double fatality at Padstow worth a read: http://www.mby.com/news/padstow-rib-...-released-1808

I'm inclined to think that your extra large load and its positioning made it that much worse when it did break away.

May also be that the speed & the lift ends up with so little of the hull in contact with the water that even in a straight line it can make the handling unpredictable & hitting a wake or wave could cause unexpected problems.
Being a cathedral hull dory I notice this on my own boat & it's a too fast for the conditions issue.

Yes, the 250 is the max size allowed. I believe 6k would be considered redline for this engine. The boat does not cavitate with tight turns. I tested the boat again with only myself and the chine walking was minor, agreed the issue I had was too much weight on stern, lesson learned.

I still would like to upgrade to a stainless prop. My research indicates Yamaha Salt Water series would be a good pick, sizing seems to range.

[Jimboat]

here's some more info on chine walk... https://www.rib.net/forum/f36/advice...tml#post362579