Rpm Help, Prop selection advice needed.

[exceed]

Hey guys,
I have a 198dlx Carolina Skiff with the 115 yamaha 4 stroke. I have been running a 3 blade Solas 13 1/4x17P prop for a couple years and have started getting into watersports and I purchased a 4 blade Solas amita4 13x15p prop. The break down is this my 3 blade gets 41 mph by GPS at 6000 rpms(perfect rpm range for my motor,6000 max.) My amita4 is hitting my limiter which is bad but my hole shot and turning are awesome, so 6200 at 33-34 mph so quite a bit slower. One thing I will add is I was getting tons of ventilation out on my 3 blade which made me want to go with a 4 blade even more and when I got my 4 blade I was getting venting also mainly on turns. I lower my motor one bolt hole and it has corrected all my venting on turns and taking off with both of my props they bite a lot harder in the turns now especially with that 4 blade.

My question is I am wanting to purchase the Solas Titan4 in a 17p and I am reading where the Titan series have more cup,rake and the blades may be more aggresive.

Final thought, the amita4 is a great prop night and day faster on hole shot than my 17p prop which is what I want but at the same time I would like to keep my rpms under my 6000 mark or a little over(I can always pull back a hair.) So if I want as close to 6000 as possible and as much hole shot as possible do you guys recommend the titan4 17 or another 15?

Break down for the skimmer/trolls.
13 1/4x17p 3 blade solas 6000 rpms at 41 rpms
13x15p 4 blade solas amita4 6200 rpms at 33-34


Thanks

 

[steelespike]

Re: Rpm advice needed

Re: Rpm advice needed

Normally you would only drop 1" in pitch going to a 4 blade.
It appears a 1" increase in pitch would reduce the rpm about 200.
I think the speed loss is from the 2" drop in pitch,the drag of the 4 blade.
and some loss of bow lift.
Scattering around to different props can confuse and make measurable results harder to get.
A prop shop could add an inch which should get you 6000 and maintain speed at minimal cost.
The titan seems like an expensive gamble at this point.

 

[exceed]

Re: Rpm advice needed

Re: Rpm advice needed

Normally you would only drop 1" in pitch going to a 4 blade.
It appears a 1" increase in pitch would reduce the rpm about 200.
I think the speed loss is from the 2" drop in pitch,the drag of the 4 blade.
and some loss of bow lift.
Scattering around to different props can confuse and make measurable results harder to get.
A prop shop could add an inch which should get you 6000 and maintain speed at minimal cost.
The titan seems like an expensive gamble at this point.

Yes I have actually thought about having a shop add a inch to get me down to 6000 rpms. One thing I did not add is that I do beach my boat a lot considering it is a flat bottom skiff which is why I was thinking of the Titan 4.

The Solas website says that the titan4 is a more aggresive prop that adds more stern lift is a high rake blade with large cupping which the amita 4 did not have any of those features listed. By my calculations if I went to a Titan4 17p I would max out at 5800 rpms, is this correct?

 

[exceed]

Re: Rpm advice needed

Re: Rpm advice needed

No one else has any advice? I know we have some bright individuals on this board.

 

[steelespike]

Re: Rpm advice needed

Re: Rpm advice needed

I found a test with similar pitch props but larger boat and motor. Original 17" al had 17% slip at 37.6 mph.
15" titan 4 blade did 39.2 @ 5475 6% slip. Even though the titan had much better grip likely loading the motor more
the rpm went up about 225.Not sure what this means for your setup but it does seem that you would need to go with a 17"
or you'll be back in the same boat with your rpm. One reason they had a nice improvement in speed was the old prop had 17% slip.
You are at about 8%. The test was a 20 ft boat with a 175 So we are a little bit apples and oranges.