Sort of a re-post with more details

[terrymiller1973]

I had posted my questions in the Yamaha and Suzuki forum prior to seeing this one so please forgive me if this is acceptable. Sorry about the edit guess to early in the morning now for the question. My WOT is 4600 I have read that it should be around 5500 is this correct, if so what prop should I try to get me close to this. Some other symptoms are that once the boat comes off WOT it start to squat in the water badly like it is trying to plane out again no matter how I trim it. The only way to get rid of the squatting is to use way to much trim tab to force the bow down some.

1990 238 Pro line WA, 8'6" beam
1990 Yamaha etld 200 on a 2' Gil bracket
weight fully loaded 7000
fuel 100 gallon
wot 32mph @ 4600 gps checked
22mph @ 3600
current prop says 19-M, 3 blade aluminum
could not check if the cavitation plate is above the hull or not due to being in the water currently.

any other needed information I will be glad to try and answer if I know it.

 

[terrymiller1973]

Re: Sort of a re-post with more details

I figured the prop slip just to make sure I am doing it right here are my results.

Motor Rpm / Gear Ratio
4600 / 1.86= 2473.11828

(Prop Rpm*Prop Pitch)*5)/5280
(2473.11828*19)*5)/5280 = 44.49739

(Theoretical Speed - Real Speed) / Theoretical Speed
44.49739-32.4= 12.09739/ 44.49739 = 0.27187 or 27%

So I know that I have a lot of prop slip but how does that equate to the size prop that I need to replace it with. Would I just do the math for each pitch prop? If so a

15 pitch is 6.13%
16 pitch is 11.39%
17 pitch is 16.65%
18 pitch is 21.91%

If the math is correct I would assume that the 16 would be the best because it is below 15% and above 7% is this correct.
I still have the problem of knowing the diameter all the hub said was 19-M can anyone tell me what that means in relation to what I need to know.

 

[BaileysBoat]

Re: Sort of a re-post with more details

Hey Terry,

That boat is rated for 300HP? A little underpowered. How high is the engine mounted. I would raise it up a hole or 2 and test again.

The 19M is probably the stock aluminum. I went from a 19M to a 17p Turning point Huster and gained 400 rpm.

You might need to go to a 15P.

 

[terrymiller1973]

Re: Sort of a re-post with more details

I agree with the boat being underpowered and plan on a repower just dont have the funds right this second. Not sure how high based off the transom I cant remember from when it was on the trailer. The mounting bracket holes are aligned with the bracket holes, it does not stick up above the bracket. The cavitation plate if I remember correctly is either even with the hull or maybe an inch above.

 

[trendsetter240]

Re: Sort of a re-post with more details

I am not positive on the WOT RPM for that motor. I believe for that setup you will need a 15p prop and likely a 4-blade to help with the lower speed cruising.

The solas amita 15p 4-blade will give you a lot more thrust than your current prop. You have a heavy boat that is underpowered. The right prop should make a world of difference to how it rides.

Is the boat stern heavy? You might want to try a Solas HR Titan stainless 4 blade if you have the cash. I use one on my boat and it provides excellent lift and power in the mid range.

Getting more of that heavy boat up out of the water will reduce the drag and provide better performance.

You could expect around 5300RPM with the Solas Amita 15p and about 5200 with the HR Titan SS at WOT. Either prop will be much better than the stock 19-m.

 

[terrymiller1973]

Re: Sort of a re-post with more details

I have thought about the 4 blade but I am definitely staying away from the SS. I live in the Florida Keys and the area I have to go through to get to my dock can be kinda skinny water at times for my boat.