Stainless prop

[Esox_Magnum]

Toying with the idea of a SS prop. Currently running an Alum 13.25x17 right at 6000 RPM on a 115 merc pushing a Skeeter S-135 17' deep V fiberglass boat. Best I have done on GPS was 42 but 40 is more the norm, holesots are good so do I stay with the 17 with a SS and sacrifice some on the low end or drop down to a 15 or 16. What will be the advantages of the SS? Will I save anything on fuel or just better preformance or even worth trying??

[LMITOUT]

At first blush I wonder if you shouldn't try a 18" SS with those RPM's.

[solbes]

You didn't say what type of Merc 115, but I'm assuming it's a newere 4S with 6000 max rpms. If so your aluminum is dialed in perfectly. Also is this with a light load? If so that's also ideal.

Assuming 6000 rpm max, I would try to drop an inch in pitch when moving to stainless. If you are switching to a prop with significant cup or rake, drop 2 inches of pitch.

If you do not experience blow out now, you may be able to move your merc up a hole or 2. If so, that will increase RPM's by 100 per hole. So you could theoretically run a 17 stainless with good cupping if you moved up 2 holes (or maybe even 1).

[JohnMickish]

I run a 115 carbed 2 stroke on a 1775 Pro V, it came with a 19 pitch aluminum prop and I swapped it out for a 17 Apollo stainless prop. My max RPM and speed stayed the same (I am guessing due to the aluminum prop deflecting a bit at high speed?) but my holeshot and boat control increased dramatically. I used to get blow outs in the corners and when trying to keep the bow high in waves to stay dry. Changing props made it a different boat. Your boat is a little heavier than mine so any issues you have should go away as well with a change to stainless.

[wastewaterguru]

I would borrow one first and try it out. Stainless is a different animal. Funny story since dropping a pitch or two and switching to stainless usually gains a couple mph as well.

I know when I bought mine I tried 4 different props and ended up dropping 2 inches of pitch but going with a larger diameter.

[Esox_Magnum]

The 115 is a vintage 1991 2 stroke 4 cylinder. Not a huge load a couple hundred muskie baits is about it and 2 guys at full load. Not realy any problems to speak of other than wanting the best preformance possible. One thing I do get is blowout at midrange if I'm not fully on plane, hard to explane but it seems to loose traction when between float and up on plane.

[JohnMickish]

I think switching to stainless will fix that. They seem to have more bite. Is there a marina or boat dealer that loans out props? There are several in my area that have colored props they loan out so there has to be some in yours, right?

[Esox_Magnum]

Only 1 fishing boat dealer in the area, several pleasure boat dealers though and I think they charge you just to walk in the door LOL. I'll ask the local shop and see if he does that or not.

[Northlander]

Toying with the idea of a SS prop. Currently running an Alum 13.25x17 right at 6000 RPM on a 115 merc pushing a Skeeter S-135 17' deep V fiberglass boat. Best I have done on GPS was 42 but 40 is more the norm, holesots are good so do I stay with the 17 with a SS and sacrifice some on the low end or drop down to a 15 or 16. What will be the advantages of the SS? Will I save anything on fuel or just better preformance or even worth trying??

I have a 115 yamaha 4 stroke on a 17' Lund Explorer and run a stainless 13 1/4 by 17 Turbo that I got from Jay Soderbloom. I like it a lot. Good bow lift and hole shot and 38-41 mph.

[Esox_Magnum]

Northlander, did you notice any change in fuel useage ?

[Eric Wettschreck]

I have a SS prop I'll never use again and you're more than welcome to give it a try. If you're ever in the SW MN area give me a call, we can meet up, and I'll hand you a prop to try out.

I realize you fish IGL a lot and it's a totally different animal than the SW MN potholes I fish. I'll never again put on a SS prop as I hit a log/rock/something and the prop didn't give a bit, but my lower unit sure did and boy howdy did that suck.

Otherwise, I agree with Northlander. Get ahold of Jay, chat it up a bit with him and he'll steer you in the right direction. Dude knows what he's doing.

I did notice when I took off the SS prop and put on aluminum (after rebuilding my lower unit) my hole shot was a little weaker and I lost a couple MPH on the top end.

[Esox_Magnum]

Eric,what motor did your prop come off and what size??

[delcecchi]

I dont think you are supposed to run that motor at 6000 rpm. 5200 max is what I recall. I use a 21 pitch on a 1775 pro vee

[Northlander]

Northlander, did you notice any change in fuel useage ?

No I didnt. I do know I get way better performance. I get a better bite in corners and like I said I get better bow lift and top end.

[jigginjim]

When I bought my 690 ranger it came with a hi-5 prop, the 5 blades I have noticed troll me slower in reverse. Front is about 2.3-2.4 mph, backtrolling is 1.2-1.4 mph. since many of my days I like pulling plugs or spinners this is a great set-up. If I were all into hi-performance, I would have a racing boat, tunnel hull/ 3.6liter v-8, 17inch sstl prop, turn RPMs at 9,000. Timmy seebold move over.

[Esox_Magnum]

Havent set my boat up for trolling yet,99% of my eye trollings done at night shallow and by the bowmount, summer times its either full throttle or idle when chasing skies. Need some rails yet for rod holders and a Terrova for spring supper trolling.....

[bemidjibasser]

Stainless will give you more top end as stated and better hole shot as well due to not flexing under the torque of high rpms. I have/ had a 115 merc on a 17' procraft bass boat that I run a 21" stainless 3 blade on. No way I would run aluminum again after running stainless...

[marine_man]

I dont think you are supposed to run that motor at 6000 rpm. 5200 max is what I recall. I use a 21 pitch on a 1775 pro vee

esox - check your owners manual, the engine plate under the hood or possible the S/N tag on the midsection... delcecchi is right on here... the majority of 115's from that era ran at a max rpm of 5250...

On the other hand though, I'm surprised you wouldn't have it the rev limiter if you truly were running at 6k.

marine_man

[delcecchi]

Are you sure that engine has a rev limiter? I never saw any mention of one in any of the literature, owner manual, etc.

[Esox_Magnum]

Not 100% sure tach is accurate only works when it wants to. Guessing if I was overreving it would have hatched by now, made more than 1 20 mile run on V this year with it.

[delmuts]

Listen to the RPM's. Your ears can tell you alot. If it sounds like it is screamming it's guts out, you need more pitch/ or bigger dia.

[Esox_Magnum]

Sounds good to me Del.

[delcecchi]

With a 17 pitch at 42 mph, I wouldn't think 6000 is out of the question. Mine has a 21 pitch and is at about 5000 at 42mph. (I have that same motor).

[hydro]

I like watching these prop threads as there's a lot of mystery in selecting the right prop for a given combination. As has been said above, the prop design and pitch needs to be matched to the RPM that the motor can pull with an average load in the boat, then hole shot and top end load carrying abilities need to be compromised for the best match.

Esox, you did not give the weight of that boat, but assume that since it is glass, it is a little on the heavy side (much like my current ride). Combine that with a fishing hull design that is directed toward general performance with a smooth ride, and we can take a guess at the efficiency. Efficiency of the hull will give an indication of "prop slip" and I would guess that your combo will see about 15% slip. Could be a little more, but probably not less.

Now, I looked up your motor, and in 1991, Mercury rated their 115 at a WOT RPM range of 4750 to 5250 RPM, and it is equipped with 2.07:1 gears. I have a calculator that will give the MPH attainable with these parameters and I plugged in the numbers for different pitches and 5200 RPM which would be typical for running a light load at full throttle. For instance, 16" pitch will net 32.4 MPH, 17" will net 34.4 MPH, and 18" pitch would push the boat to 36.4 MPH, all at that 5200 RPM, 2.07 gears, and 15% slip condition.

To get 42 MPH, you would need to spin a 17" prop at 6354 RPM (and risk ventilating the block!) or use a 21" prop at 5200 RPM (Delcecchi is right on the mark on that number). These numbers assume a stainless prop, typically 3 blades, and no significant cup in the blade design. By adding cup you can lower the pitch numbers by 1" to maintain the parameters, and if you want to go to a 4 blade prop you would need to start over and reduce both diameter and pitch to maintain the same motor load.

[Esox_Magnum]

No idea on weight, but speed is verified on GPS and when the tach decides to work ( right or wrong) it will read 5800 at WOT. Boats a 1991 Skeeter S-135 look it up if you would like to know the weight,same hull as currently under the Tuffy 1700 Osprey just a different cap.