Deck boat prop opinions

[KurtS]

Hi,
looking for help / opinions on the best prop for my application.
1) Performance issue you are trying to correct.
Better holeshot and more topend.
2) Current prop manufacturer, model, aluminum or stainless as a minimum.
Piranha composite 1517a - 3 blade.
3) Current prop diameter and pitch (required).
15 x 17.
4) Wide open throttle RPM and speed with an average load (very helpful)
38 mph at 4,900 rpm.
5) Engine/drive make, model, year, and HP
Volvo 5.0GL, Cobra SX, 220 HP.
6) Boat make model, year, length and weight
1999 Ebbtide 23' FunCruiser deck boat, 4,000 lbs. + avg. 800 lbs (fuel and passengers).
I'm not too concerned with top speed, but 38 mph doesn't seem right. I'm more concerned with getting on plane quicker and keeping it on plane at slower mph - we're going to try getting the kids into wakeboarding. It seems slow to get on plane, but once I do I can keep it there down to 17mph. My previous prop was a Michigan Wheel 15 x 17 3 blade that I think the tips may have been ground down some. It had the same top end with less holeshot and 22 mph minimum plane speed. I'm thinking of getting a 4 blade, either the MW Vortex 14.5 x 18 or the Solas Amita 14.5 x 17. Any opinions would be appreciated.

 

[craze1cars]

Re: Deck boat prop opinions

I believe your Volvo has a 1.60 drive ratio.

If yes, you currently have about 22% slip. That's a lot. And I'm guessing it is because you have a composite prop. I have absolutely zero experience with composite props, but I will speculate that on a boat as heavy as yours, the blades will flex substantially under load, effectively reducing pitch, and therefore your RPMS will go up, but without the benefit of moving the boat any faster. Basically I think your composite prop may be very inefficient.

I suspect aluminum or stainless would be better for you, but guessing on a pitch will be very difficult since I have no idea how to compare composite to more conventional props. Is there any way you can borrow/test drive some used props from a local marina or prop shop?

Your RPMS are a hair high...I believe your rig wants 4400 to 4800 range.

But if I were in your shoes, I'd try to find another 17 pitch prop in either stainless or aluminum (to borrow) and give it a shot. And I think I'd shoot for a 4 blade. I suspect you'll see a small improvement in holeshot and top speed, along with a small drop in RPMS. All would be desirable. Even if that is not what happens, you'll have better data to share to see which direction you need to move.

Compared to a 3 blade, a 4 blade will usually improve holeshot, and provide more stern lift/slightly lower planing speeds. This is usually at a bit of expense of top speed. But compared to a COMPOSITE 3 blade? I'm thinking it might actually improve both at the same time...

That's a relatively small motor for a boat that size and weight...so don't expect miracles. I doubt you'll ever see much more than 40 mph out of it...but I could be wrong.

 

[KurtS]

Re: Deck boat prop opinions

I just purchased the boat. It came with a Michigan Wheel 15 x 17, 3 blade prop. After taking it for a test ride the seller forgot to lift the outdrive and took a little off the outside edge of the prop. When we test drove it I didn't check for top speed but I did check the minimum speed to keep on plane. It was the same 18 mph as the composite prop. As for the boat weight of 4,000 lbs, this was from the manufacturer. I don't know if they use full tank (70 gallon) or empty tank for this number.

 

[craze1cars]

Re: Deck boat prop opinions

Seems that a slower planing speed is a priority of yours...

Frankly I don't think you'll get a boat of that size to plane at much less than your current 17 or 18 mph, especially with only a prop change. You might get lucky and knock another 1 mph off at best.

Adjustable trim tabs would be far more beneficial, possibly in conjunction with a different prop, if slower planing speed is one of your main concerns.

 

[KurtS]

Re: Deck boat prop opinions

Thanks for your help craze1cars. I'm happy with the speed I can keep it on plane, it's getting it on plane that takes too long. Once there I can back off the throttle and stay on plane at a speed I'm happy with. I thought I could be capable of around 43 to 45 top speed and still keep what I have on the lower end. Of the props I was considering (MW Vortex or Solas Amita), which one would you recommend?

 

[craze1cars]

Re: Deck boat prop opinions

I think you're looking in the right general direction with a 4 blade. I am a little concerned that you will purchase a 17 in either model, and you'll find a dramatic change in your RPMs when compared to your composite and the 3 blades you've previously run. So I still strongly suggest a test-drive of a borrowed prop thru a marina or local prop sop, or some type of opportunity to return or exchange a prop (rare in the mail-order world). Mail-order experimentation can get expensive.

I have been very pleased with my Solas 4 blade (mine is Stainless). I had to go to a lower pitch than I expected with it to maintain my RPMS. I have zero experience with Michigan Wheel Vortex, and no specific experience with the aluminum Solas Amita.

So I will defer to others for such a specific recommendation between models.