115hp prop question

[pyroom]

Hi,

I've got a 2009 Crestliner 1700 SpotFish with a 115hp Mercury engine, and I currently get around 45mph top speed on a good day (GPS), at about 5200 RPM. On the side of the motor, I saw that WOT is 6400 RPM. The boat struggles to get on a plane when it's loaded down, but eventually gets there and usually has sufficient power afterwords. I was just wondering if there was a prop that could achieve a higher top speed (say 50MPH) without losing any low end power. I'm at around 1400 feet elevation. All I know is that I currently have a black three blade prop with a sticker that says 14 on it. When I bought the boat the guy told me that with this specific prop, for maximum performance you should trim the motor so the top of it is out of the water and so it make a really annoying sound.

EDIT: Everything is stock on the boat, and the speeds were with just me, 140lbs and nothing else in the boat.



I remember last year, late fall a few days before the lake froze over. I gave the boat about 7/8th throttle and it screamed up to around 6000 RPM and I backed off right away thinking I was going to blow the motor. If I recall the GPS read a little over 54MPH.

 

[steelespike]

Re: 115hp prop question

Is it a 4 stroke motor? If 6,400 I would think 4 stroke.The size of the prop will be stamped on the barrel near the base of the blades or under the prop nut.I don't think your elevation will effect things much.You may have to make a few runs with just you, trim to the highest speed and and usefull rpm and get the figures to us with the prop size.Increase trim slowly and let it settle a little.

 

[pyroom]

Re: 115hp prop question

It is a 4-stroke. I will have to do the runs tomorrow, although when I was out tonight I couldn't get the boat past 32mph for some reason.

 

[steelespike]

Re: 115hp prop question

Some for strokes will limit power if oil pressure is low or it thinks the oil pressurer is low,also may reduce power if temp rises.

 

[pyroom]

Re: 115hp prop question

Well I did several runs today with 2 guys (around 400 pounds for both of us) and minimal gear. Both live wells were empty, boat was drained, etc.

The boat is likely waterlogged from the amount of rain we've had the past 4 weeks, I noticed the floor was still quite wet from the good thunderstorm yesterday. 1/2 tank of gas which is a mix of 10% ethanol/sea foam and premium gas. Gas is well over a month old. Had a good 30MPH crosswind during the whole test. When I pulled the motor up to look at the prop I noticed an awful lot of algae on the boat - I'll pull it up to clean it next week sometime. All speeds were with GPS. I put the boat to a plane and slowly took it up the full throttle, then I very slowly increased the trim until I felt a loss in power (the prop started to come out of the water). Water temp was 70, air temp was 90.

6 runs were at 33MPH @ 4900 RPM (against the current)

2 runs made it up to 35MPH @ 5000RPM (with the current)

Earlier in the year I didn't have a problem getting the boat up to 40 MPH at around 5300 RPM. (when I said 45 @ 5200 RPM in my previous post I was going by the gauge, not my GPS.)

I'm assuming the prop currently on the boat would be for optimal fuel economy, because the dealer assured me this boat would receive almost identical fuel economy at 30MPH (4500 RPM for this boat) as my old 40HP fishing boat did (and they were right for the most part).

It looks like the propeller says "H 13 25x 17p", there is also a "P" and an "M" ? - below are pictures:

 

[pyroom]

Re: 115hp prop question

bump

Did the mercury prop selector and it spit out part number 48-17314A46

Vengeance SS 3-blade 13.375" 14.0 pitch

A friend of mine also has a 12 3/4 " x 21" prop off of his 115hp that he will sell to me for a good price (stainless)

I'm going for top speed, but I wouldn't mind getting a little better hole shot for tubing and stuff.


Any suggestions?

 

[pyroom]

Re: 115hp prop question

Washed the boat today, now with a full tank of gas I get 36mph at 5000RPM and occasionally I saw 40mph at a little over 5100RPM on my GPS. This test was also done with two people on a very hot day - over 100 degrees. No wind.

Can anyone verify what H 13 25x 17p means? I'm guessing it means 13" prop with a 17 pitch?

From what I've been reading around here, it sounds like I should be able to talk to my dealer and test a few different props before I buy? I would really like to see 50MPH if that's possible.