Any prop gurus out there?

I need to pick up a spare prop for a Canada trip this year… so I am just doing some preliminary research. It might make sense to put on a better prop and keep the stock one as my spare.

I got a new boat last year that was advertised to go 43-45 with a regular Merc 115. I upgraded to the ProXS 115 and could only get 35. That’s as fast as I need to go… but it leaves me wondering if the stock Black Max is not a great match or is just an underwhelming performer.

Here is what I see when I plug all of my data into the Mercury prop selector. That Black Max is the exact prop that I have.

What is not clear to me is what I’m gaining or losing between these. I wish someone could tell me “if you switch out to the 4 blade Spitfire you’re going to jump up on plane faster but lose a few MPH” or whatever the case may be.

Any pointers would be appreciated!

thanks

So, the info needed here is:

The specs of your current prop (diameter, pitch, # of blades)
How many RPMs you’re turning at WOT (and the recommended top end for your motor)
How’s your hole shot? Bow lift? Any other issues?

If you drop in pitch, you’re going to get better hole shot but lose on the top end. If you go from a 3-blade to 4-blade, you’ll typically lose a little on the top end but have improved hole shot, bow lift, and “bite” (i.e. the prop is less likely to blow out in corners).

If your current hole shot is good and you’re at or above the recommended WOT, you can increase the pitch of your prop to increase the top speed (keeping in mind that you’ll sacrifice a bit of hole shot).

You are trimming your motor at speed, correct? Once you’re on plane, you should be trimming the motor up. This lifts the bow and leaves less hull in the water (which decreases drag on the boat).

Hey Ralph. The current prop is the top line on that screenshot. So 3 blades, 13.25 diameter, 17 pitch.

The Mercury WOT spec states 5300-6300. Unfortunately my memory is not good enough to remember what I was getting (last year) and I haven’t been able to rip around at WOT yet this spring. If that data is crucial to making a decision we’ll have to wait. I do have VesselView so I can get solid digital data.

I was trimming up on plane. I felt like the hole shot and bow lift were good. No concerns other than top end.

Not in your area but one of the guys at Rapid Marine in Ham Lake is a prop gurus and helped me out. I would go stainless on the replacement it will improve your hole shot a bunch and make the old prop a spare.

Sorry, your screen shot isn’t showing up for me.

Yeah, the RPMs at WOT are pretty critical. Just a hunch that you’re probably running pretty high on the RPMs, so you could increase your pitch, but that is just a hunch without the complete info.

Is your speed measurement with GPS?

Unfortunately, props are kind of a trial and error game.

I had a Laser II SS prop (19p) on my 115 ProXS and 18ft Kingfisher when I bought it. I wasn’t pleased at all with the performance so I put a 17p Spitfire X7 on it and it was a HUGE improvement. I gained about 400 rpm but more importantly, the holeshot was dramatically better. Also I can trim up to max and it doesn’t blow out and it also handles great. I’m still only maxing out at 5800-5900 rpm so I bet I could’ve actually went with a 15p.

Current top speed is about 42-44mph @ 5900 rpm

Also make sure your motor height and trim are optimized, those 2 things are big factors as well.

Yes, my speeds are GPS.

That’s good data 3Rivers, thank you.

I won’t make a decision until I get to test WOT RPM again.

I did notice Solas makes an exact spec prop as the Spitfire X7 for half the cost: https://www.deepblueyachtsupply.com/solas-hr-titan-1453-130-17-boat-prop

I’m just not sure if there’s any proprietary hub/exhaust crud I would need to account for.

Make sure when you go out to test WOT you have the amount of weight/gear you will normally have with. Your boat will sit lower in the water and have more drag at WOT the more weight you have in it. Thus effecting the RPM. Too high of a pitch prop will not only hurt your hole shot but can cause you to lose top end.

What boat you have?

Tracker V-175 WT

Won’t necessarily help but I can share my experience in case it does. I was struggling with low RPM’s (2001 4stroke 90 Merc on a 1600 pro sport) and terrible hole shot with the 13″x19p prop that was on it when I got it (used). I happened to work with a guy who had that same aluminum spitfire on your list and it made a man out of that thing. Way better hole shot and now I’m in (the low end) of the listed WOT on the seldom occasion that I do let ‘er rip. That was with an aluminum prop, haven’t convinced myself to drop the money on a SS one yet, could probably improve performance even more with tweaking but it’s worked good enough that I haven’t bothered.

Had a 2016 1775 Lund pro guide with a Merc 90 hp a while back, and ran a 17″ Spitfire x7. Don’t remember exactly, but if I remember right I was about 42 mph at about 5800 rpm, and that was with 90 hp, not 115, and a boat apx same size. Thinking about it, it might have been closer to5700 rpm. Also while Solas makes a 17″ prop, don’t even begin to compare that prop to a Spitfire x7. A good 17″ prop should easily put your boat in the low to mid 40’s. My exact #’s should be on an earlier posting of mine, and if not on this forum, are posted on walleye central, look it up.

I feel some props (almost always) out preform others when fitted to the boat correctly.

best luck prop has been the trophy plus it is a fantastic all around prop with great hole shot especially with 17-19 foot tiller boats

I have a 17ft ranger 207t (same hull as the new crestliners) with a 75hp merc and a 17 pitch trophy plus will run 38-40 @5800 rpm could prob get more speed but i prefer holeshot and torq

I have seen multiple sites stating that the Spitfire X7 is no longer made / discontinued.

You have mail.

mmitties wrote:

You have mail.

I do?

Look at the top tool bar next to the logout icon and if you have a picture of a envelope, click on it, he probably sent you a PM.

Call marks prop shop in Stacy MN. They will have all your answers. I called yesterday and they knew exactly what I wanted, needed and had it in stock

John Rasmussen wrote:

Look at the top tool bar next to the logout icon and if you have a picture of a envelope, click on it, he probably sent you a PM.

The PM came in hours after his post. I was definitely confused for a little while.

Anyways. I’m not sure if I’m going to drop $600 on a prop… one thought I had was $200 Spitfire aluminum vs $300 Solas stainless. That would be an interesting bake-off. I may see if I can buy both (from places that would take returns) and try them both one day and keep the one I like.

I run the vengeance in I think a 18 pitch, with a very similar boat and it allows me to get a good hole shot and has enough power to handle rough water. My only complaint would be top speed, I have thought about going up a size just to improve that but at the end of the day would rather have the better ability to be safe when its rough.

Switching to a stainless prop will help for sure. May need to raise your motor a bit too. A lot of boat shops will allow you to test a prop on your boat before you purchase. This way you will know if it will perform as you wish prior to buying. Maybe look into this. I am sure the boat shop and folks on here can get you pointed in the right direction as far as pitch. I put a Vengance 18 pitch on an 80 HP Merc I had years ago, much improved over the Black Max that it came with. But every boat and set up is different.

Bearcat89 wrote:

Call marks prop shop in Stacy MN. They will have all your answers. I called yesterday and they knew exactly what I wanted, needed and had it in stock

Mark is a family friend, and I’ll vouch he’s the best around. If your prop is damaged or even if it just needs a little tweaking he’ll get it done and at a great price.

sipple31 wrote:

Anyways. I’m not sure if I’m going to drop $600 on a prop… one thought I had was $200 Spitfire aluminum vs $300 Solas stainless. That would be an interesting bake-off. I may see if I can buy both (from places that would take returns) and try them both one day and keep the one I like.

The aluminum spitfire is an excellent prop. With the 115 ProXS you will want a 13×17 Spitfire. Remember with the spitfire, no need to change pitch from whatever your 3 blade is. I actually prefer my Turning Point Express Mach 4 to the spitfire, but the spitfire is my backup. Oh, and the Quicksilver nemesis is the EXACT same prop as the merc spitfire, with a lower price tag. Just FYI.

I would not run a 3 blade with this motor. I run 42-45 mph all day with both the spitfire/nemesis and my turning point. The difference is the turning point is 13.25 diameter and bites better in turns.

I called Mark’s Prop Shop and he recommended going with the Aluminum Spitfire – even though he doesn’t sell them. I appreciated the approach of not trying to corner me into something he could sell me.

I did finally get the boat on a lake this past weekend and opened it all the way up. I topped out at 37mph@5500 RPM.

The Black Max washes out terrible on corners. So I’m just hoping the additional “bite” of the Spitfire fixes that and also adds some bow lift to gain some top-end speed.

I’ll report back.

Max RPM on on this motor is 6300 per Mercury’s website and my manual. IMO the sweet spot if anywhere from 5900 – 6300. I prefer not to red line it, and I really can’t get above 6200 with my setup so it works.

he 17p sptifire will solve your problems 100% without a doubt, but will still blow out if you try to corner fully trimmed up. I run a 17p turning point express mach 4 on mine. The difference is this is a swept cleaver blade geometry and it is 13.25″ diameter rather than 13. That extra diameter seems to help me corner at WOT without blowing out.

If you still have issues, your hull just isn’t as fast. I don’t know anything about Tracker’s deep V hulls but I doubt this to be an issue, because their 21ft grizzly mod V is impressively quick even when it’s being pushed by a 90 horse merc.

But yes in short, save the black max as a spare to get you home in case of emergency. They suck. Might as well keep an extra hub in the glove box too, because if you smash up the prop such that it’s unusable, it’s pretty likely you damaged your hub too. Cheap insurance.

One thing I didn’t see mentioned above, and I mean aboslutely no offense by this: when you are running at “WOT”, are you also trimmed all the way up?

I mash the throttle with motor trimmed all the way down. Once I’m on plane I dial it way back on throttle and basically control my RPM’s using only my trim position. Trim up = higher RPM at a given throttle position. I like to run around 3800 rpms for cruising. When I do a WOT run it’s full throttle, full trim until I start to blow out (you can hear it and feel it), then back down slightly until RPM’s are dialed at ~6200

(Didn’t realize I already answered the same thing before)

KPE wrote:

One thing I didn’t see mentioned above, and I mean aboslutely no offense by this: when you are running at “WOT”, are you also trimmed all the way up?

I mash the throttle with motor trimmed all the way down. Once I’m on plane I dial it way back on throttle and basically control my RPM’s using only my trim position. Trim up = higher RPM at a given throttle position. I like to run around 3800 rpms for cruising. When I do a WOT run it’s full throttle, full trim until I start to blow out (you can hear it and feel it), then back down slightly until RPM’s are dialed at ~6200

I certainly do trim up and the RPMs climb… but I don’t trim all the way until it blows out every single time. My boat does have a trim indicator and I should put a little mark or something where the ideal WOT trim is at.
Thanks for all the advice. It’s been helpful. I’ll report back once I rip around on the new prop.

The 19pitch spitfire is actually a smaller diameter than the 17. I’ve found that I get the same or even higher rpms with the 19 than the 17.

I wanted to circle the wagons on this. The Spitfire added some “grip”, maybe a little better bow lift, but I did not notice a difference on the top-end. Same RPM, same top speed.
Ultimately, I’m happy with my rig. I’m not chasing a couple MPH… especially with gas prices being what they are.
My only thought is that at my next annual maintenance I may ask them to confirm that full throttle is actually being reflected on the engine side.
Tight lines!