Newbie prop question

[irv64]

Relatively new to the forum and very new to prop questions/issues.
I have an 06 Lowe 165FS with an 07 Merc. 90hp 4 stroke. I am pretty happy with everything so far but I would like a little more oomph out of the hole especially when tubing/skiing and I would like a prop that won't cavitate so much when turning? I have to trim down quite a bit while turning.(could it also be the design of the hull?) I currently have a 19 pitch 3 fin aluminum on there which gets me 47 on the speedo(probably not too accurate?) at 5500 to 5800 rpm.
I was told to use an 18 pitch 3 fin stainless and it would be a night and day difference? It would get me out of the hole better and it wouldn't cavitate near as much on the corners? This is what my dealer says anyways. I was told they are about $750.00 bucks up here in Canada? I also asked him about going to a 4 fin prop and would that be better? He said it would get me out of the hole better but would be no good in rough water when the prop comes out, said it would be very hard on the engine? Just looking for some other people's input as I know very little about props as you can tell. Thanks in advance...........Irv64

 

[Texasmark]

Re: Newbie prop question

I have the 2 cycle version of that engine. It has a 2.3:1 gearbox which allows you to turn pretty good pitch in your prop.

If your boat has a "keel" that answers a lot of your question. Alum boats that are welded (like mine) use a piece of angle alum and make a v all the way down the boat stopping at the transom. The purpose is to cover up the center weld but it adds turbulence in front of the prop making blowouts common in turns.

I have a 17' BB that weighs on up there for an alum. I have a stepped hull. If you look at the transom from the rear, from chine to keel, there is the boat hull, then they bent the material into 1" steps, 3 times before getting to the keel. So it makes a pad and the faster you go, the fewer the pads you have in the water and hence less friction allowing for disproportional increases in speed and engine rpms. Then there is the keel......all this blab is for developing my pedigree for offering advice on your question.

I have run 17, 21, 23, and 24P props on the boat to 50 mph GPS with the 24P at 5600 rpm's. All but the 23 were Ballistic SS. The 23 is a Turning Point Hustler alum. It's ok for alum, but even though it is a high perf alum, it's still an alum and the thick blades cost you performance.....but if you gotta have an alum, due to water hazards, then by all means I think it's a great prop.

If your Lowe boat is what I think it is you have a pretty good V bow changing to a slight v at the rear with no steps. Weight would probably be about the same. I was alone with my tests, 10 gal fuel, 3 size 27 batteries, tackle, and a bimini top stowed. I would expect your drag (because of no pad) to cost you 2-3 mph over mine.

With that said I'd certainly invest in a SS prop and they have some good ones forsale herein for a great price.....like the Stiletto @ $280 US for a new 3 blade SS. In 19P would probably be perfect for your boat assuming you'll load up with 3-4 folks and one or two would be in the water when tubing. The 19 will have a cup which is said to equal an additional inch of pitch, but the prop will be so efficient, you will not have a problem with that. Even though they are theoretically the same 19"P the performance will be noticeably better. On the hole shot see below for a great improvement in that.

The Stiletto has cupping to help you to hold on to your rpm's in turns and ports to help you blast outta da hole; no need for 4 blades which hurt you on top end. Thin SS blades with progressive cup for efficiency and proper boat attitude.

If boating alone, you will have to cut your throttle to maintain your rpm's.....I think the 4 strokes like 6000 for running.......with your boat fully loaded you should not have a problem maintaining that.

Next choice is 21P as that is what I use (on occasion when the wife is along and the live well is full of water) and it's very gutsy; like I can be coming off plane, let the boat settle in the water (around 16-18 mph), with the trim still out like it was when I was running, and hammer down on it. It pops out of the water, plenty of thrust......but I think you will be carrying too much load for that when you are skiing/tubing so that is why I think the 19 is better.

I ran over to the prop calculator and your are correct about your speedometer not telling you the truth. My speedo indicates 2 mph too fast at WOT (proven by GPS) and I think yours is worse than that.

Using the prop slip calculator, 2.3 gearbox, 19P (non cupped alum), 5500 rpm's your max speed with no prop slip (impossible) is only43 mph. With a reasonable 15% for your current rig/setup yields only 37.

In calculating the perf of the SS, I upped the rpms to 6000 cause I think you'll get there and your lossless speed is now 49. With the higher speed and less boat in the water, hence less drag, I dropped slip to 12% and your net speed comes out at a real 43. (I used 12% because that's what my boat has....yours may be higher so you may be down at 40-41 as I mentioned earlier due to hull design.)

Hope this helps.

Mark

 

[steelespike]

Re: Newbie prop question

Texasmark you obviously did some excellent research.I'm not an expert but 3 things come to mind,one,Generally when going from aluminum to stainless at the same pitch you will lose rpm.two Generally speaking a 4 stroke will require a little less pitch than a similar 2 stroke,3 A 4 stroke needs to run at or near
its max rpm.irv64 I think is presently barely making his max rpm.I think a stainless 17 would keep the rpm and help his hole shot and top end together.
I think a 19 ss will dissapoint in hole shot and max rpm.
Just some hopefully helpful generalizations from an old timer.

 

[irv64]

Re: Newbie prop question

Excellent info TexasMark! Thank you so much. I am leary of a stainless prop due to the hazards in my lake but I would like one for the performance gains and boatability(is that a word? LOL) I believe my engine/prop has no shear pin? Is that correct? So if I do hit something good, can I expect some severe engine damge?
Thanks for the heads-up on the Stilleto, sure is a lot cheaper than what I can get one for up here! I will be sure to check them out. Thanks again for putting so much effort into answering this post! It is greatly appreciated........Irv64

 

[Texasmark]

Re: Newbie prop question

Steel. Take the boat I mentioned.

I was having "clutch dog rattle problems" with my 24P XP Ballistic. In gathering info, it seemed that the weight of the prop and high pitch, along with an engine with only 3 cylinders made for the problem.

So Turning Point had their Hustler's on sale one day and I bought a 23P which was the highest pitch they had. Being alum I figured that would solve the weight portion of the rattle issue. You can pull up both props up on www and read their fine points. The only real difference between the two is one is made of alum.

You would expect the alum to gain you 250 to 300 rpm's as it is one inch lower in pitch. Both are cupped so that part is a wash.

That prop cost me 3 mph and 600 rpm's not counting the added rpm's I was supposed to experience. I was running 50 at 5600 with the SS and this cut me to 47 at 5000. Obviously I can't use the prop as the engine is rated 5000 to 5500.

Only thing I can attribute it to is the thickness of the blades.

I agree on 4's liking to run higher rpm's (per guys on here who apparently know) but I mentioned that. Course I like to run my Mercs up to 6000 so it's a no brainer for me.

Gotta remember this is a 2.3 gearbox. Like I said before, if you haven't run them they take more prop than the normal 1.64 to 2.0 that most other engines run in their gearbox.

Since I have a very similar rig, and have spent a lot of time fooling around with this boat....like 4 props for it as I mentioned, I felt qualified to answer his questions.

Glad you got your ID back.

Mark

 

[irv64]

Re: Newbie prop question

Is this the prop you mean Texasmark? Also do you know why some props etc can't be shipped to Canada and other things can? Thanks again.....Irv

Advantage I Stainless Steel Propeller for Mercury, Mariner, Sea Ray Mercury & Mariner 90 HP (2 & 4-Stroke) (Thru Hub Exhaust & 15 Tooth Spline) 1-800-914-1123
Call for Customer Service

? Marine Store


Representative Photo Only
Price: $283.99
Compare at: $369.00
You Save: $85.01 (23%)



Prop Specifications:

SKU: 11319
Pitch: 19?
Diameter: 13-1/4?
Blades: 3
Rotation: Standard
Material: Stainless Steel

Usually Ships Within: 1 Business Day(s)




Promotional InfoProduct InfoShipping InfoReturn

 

[Texasmark]

Re: Newbie prop question

I wasn't able to see any pictures, but your numbers are right and I think Stiletto calls it the Advantage I.

Know nothing about shipping across the border. Would think that iboats would have a way for you to get parts in Canada.

HTH

Mark

 

[irv64]

Re: Newbie prop question

Thanks TexasMark, it is called the Advantage1. I wrote them (Iboats) earlier in the week asking them about another prop (before I got your info) and they said they couldn't ship it to Canada? They didn't provide a reason why, they said to try another product? Maybe it has something to do with metal parts? I will try this prop and see if I can get it but I have my doubts. Thanks again for all the info and your hard work, I appreciate it! I will see if someone can get it for me?...........Irv