Advice on propeller replacement

[FilUlf2011]

Good morning to everyone and in particular to Boscoe99.

A question about propellers: on my 1996 Pro-V 100 2 st. (it’s an european derated version of the classic Yamaha V4, 115 - 130 ) with the propeller currently mounted, an original Yamaha pitch 17 in aluminum (I do not know if the diameter is 13,00 or 13,25) the engine rpms with normal load are slightly out of specs (at WOT they should be around 5.500 while they get to 5.700 rpms).

I am therefore looking for a slightly “longer” prop with an higher diameter and/or pitch.

What diameter/pitch should I look for?

For example: if I buy an aluminum 13.25 x 17 by SOLAS, what happens? Do I lose or gain rpms (or they just remain the same) considering that the shape of the blades in OEM Yamaha props is different (Yamaha adopts a "semi-cleaver" while Solas has a more traditional shape).

I have consulted Solas and they tell me that with their 13x19 (in aluminum) I would lose about 600 r/mins, which is too much for my needs.
So, should I go for the 13,25 x 17 by Solas?

Small addition: Solas also produces propellers with the same shape as the Yamaha OEMs (they’re called “AMITA 3 – OEM Blade style”). But I do not know what would happen if I take their 13 x 19 Oem Style. How much would I lose in rpms?

In short: do you have any advice to give, based on your experience?

[99yam40]

all of this depends on how loaded the boat was when running at 5700.
change the load and you will change the WOT RPM with the same prop

[boscoe99]

Good morning to everyone and in particular to Boscoe99.

A question about propellers: on my 1996 Pro-V 100 2 st. (it’s an european derated version of the classic Yamaha V4, 115 - 130 ) with the propeller currently mounted, an original Yamaha pitch 17 in aluminum (I do not know if the diameter is 13,00 or 13,25) more than likely it is 13.25" the engine rpms with normal load are slightly out of specs (at WOT they should be around 5.500 while they get to 5.700 rpms). IMO 5700 RPM is not too far out of specs. This assumes you are seeing this RPM when the boat is loaded, the throttle is wide open, and the engine is trimmed up only to the point of maximum efficiency, and no further.

I am therefore looking for a slightly “longer” prop with an higher diameter and/or pitch.

What diameter/pitch should I look for? What type of boat and what is its top speed?

For example: if I buy an aluminum 13.25 x 17 by SOLAS, what happens? Do I lose or gain rpms (or they just remain the same) considering that the shape of the blades in OEM Yamaha props is different (Yamaha adopts a "semi-cleaver" while Solas has a more traditional shape). If the blade shape/size changes, even if the diameter and pitch are the same, then all bets are off as to what the results will be.

I have consulted Solas and they tell me that with their 13x19 (in aluminum) I would lose about 600 r/mins, which is too much for my needs.
So, should I go for the 13,25 x 17 by Solas?

Small addition: Solas also produces propellers with the same shape as the Yamaha OEMs (they’re called “AMITA 3 – OEM Blade style”). But I do not know what would happen if I take their 13 x 19 Oem Style. How much would I lose in rpms? Rule of thumb is (assuming blade material, shape/size remains the same) is that for each inch of pitch change changes the WOT RPM aproximately150-200 RPM. If this rule holds true then you would lose 300 - 400 RPM by going from a 17 pitch propeller to the 19 pitch propeller.

In short: do you have any advice to give, based on your experience?

Changing propellers to achieve a particular objective is trial and error, trial and error, trial and error. There is more to it than just achieving a particular WOT RPM. Different propellers will feel different. That difference might be objectionable. The time to plane can get worse. It may ventilate excessively.

If you are happy with the way your existing propeller feels, and it is otherwise doing what you want it to do from a speed and efficiency standpoint, I might leave well enough alone.

Another thing that is important is engine height? Most motors are mounted too low. First get the engine height optimized and then see about changing the propeller. Below are some photos of what your anti-ventilation plate should look like when you are at your cruise RPM.

[FilUlf2011]

boscoe99

The boat is the one in the photo (the engine is different) ... Speed at WOT should be around 38 MPH, but I could be wrong (don't use the boat since last summer) ..

[99yam40]

Sounds like you do not know the actual speed at WOT when it runs 5700.

do you have any idea how it was loaded too

[pstephens46]

Hard to imagine that boat will top out at 37mph with a 100hp motor. Looks to be 18-20 ft.

[walleye1]

It has a 150 on it.

[pstephens46]

It has a 150 on it.

I don’t think that pic is his boat. Just an example. He said 100hp in his first post.

[99yam40]

he posted this was his boat, but with the 100 hp Yam on it now

[Jason2tpa]

I don’t think that pic is his boat. Just an example. He said 100hp in his first post.

Agreed ^^^. My 2 cents...if the hull is indeed 18'-20' with 100hp-130hp hung, I have doubts he'd reach a top end speed in high 30's. Bird's eye view of that hull looks like a dry hull weight >1500lbs....and 130hp doesn't push that weight hull that fast. Be that as it may, speed isn't a reliable metric to consider when determining if your boat is propped correctly...too many environmental factors can and will affect speed.

OP states engine is turning only 200 rpms higher than spec...before investing in a new/used prop just to drop 200 rpm into spec range, I'd first verify engine height as boscoe pointed out. I'd also trying shifting weight aft, see what effect this has. And what was this 5700 measured with full/half/quarter tank of fuel...what were the conditions at time of testing...head wind, no wind, choppy, slick...?

If after verifying and testing again you are still 200 rpms higher than spec, I know mercury quicksilver makes an 18" prop. So instead of increasing pitch by 2" and risk losing too many rpms, consider an 18" SS. I faced a similar scenario, only reverse...had a 21"...dropping to 19" wasn't enough, dropping to 17" was too much...18" has me dialed in to top end spec.

[FilUlf2011]

Ok: I reply cumulatively to everyone.

Sorry for the delay due to the different time zone (I live in Italy).

First of all: as I wrote clearly, I do not remember exactly the maximum speed because I have not used the boat since last summer.

Surely the analog instrument marks over 35 MPH. I will check with the GPS in a few days when I'll put the boat back in the water.

However: the boat is a 19 footer and weighs kg. 650 and my Yamaha Pro-V 100 weighs exactly 155 kg.

Adding fuel (80 liters/half tank) safety equipment, cushions, four people on board, I would say that we are certainly over 1,200 kg of weight.

The 200 rpms beyond specifications are achieved in the above described navigation conditions.