questions on propping my boat

From my experience propping my boats from 16-19′ I’d say that a 19 pitch prop is very sufficient to give the proper RPMs and speed (don’t look for speed records, but maybe 50mph tops) for this boat/motor combo. I’ve seen 21P on boats of this nature.

Are you sure your RPM gauge is correct?

Are there any possible issues with the hull? Is there a possible hook in the hull or something that is adding stress to the motor?

Case in point…I had an Alumacraft that performed incredible until a friend hit something and damaged the hull with a slight dent. I could not believe how the performance went down….lower RPMs, speed and the hull wanted to plow.

I had a 17′ Alumacraft w/ 115 that would turn a 19 pitch prop at 5500 fully trimmed and 45 mph. Hole shot wasn’t good, so I kept a 17 pitch for 5900RPM and 42 mph.

Everything on the boat seems to be fine, and I have no reason to think the tach is off. It’s a digital model, so I don’t know a lot about it.

I think what’s going to happen is I’m going to raise the motor up another hole or two and see what happens. All we’re out is silicone and time. Sure wish I had a 17 and maybe a 21 prop to play with. But we’ll see what raising the motor does. Sure wish I had the $$ to spring for one of THESE.

Id keep raising it, I got a 10 inch manual jackplate laying around, I’d let you try it out, but I think you live a ways away, and I think most boats run out of cable lenght after a 6 inch plate….

Never did come up with a diameter for the 19 pitch 3 blade? I would serously try and find 14 X 19 3 blade stainless with a good cup and try that I just have the feeling your M prop is to large of a diameter. The four blade is way to much for your boat and motor. Normally just changing to a four blade will drop your RPM`s 200 staying with the same size prop.

Raising the motor is good on my 182TS my Opti is not raised.

Here’s the latest: I moved my motor all the way up on the transom last night, took it out today and tested it out. My top speed has gotten a bit better, up around 44 or so, but my RPMs only touched 52 once. I’m thinking I did the right thing though, would you agree? Also, I think since I moved it up, now it’s time to play with props, no? Ready for your suggestions.

Try and find 19p Tempest Plus, Ebay, Bass Boat Central might be good scources for a prop

I would agree with Kirt or for a few more $$ a 20P merc enertia as the design/thinner blades allow you to turn a bigger prop and still get the RPM’s that you are looking for.

Do you have a merc dealer around that does the prop exhange program so you can try different until you find the right one and then buy? This is the best deal that I know of for tuning…

Usually for me after I go through all this work and then trash the prop so I hope for better results for you.

Also keep in mind that the cooler air and water temperatures will allow your engine to make more hp and will run stronger than having the same load during the heat of the summer. I will always sacrifice top end for a great hole shot and good mid range acceleration – but that’s me.

Good luck!

-ted

Nice, looks like it’s prop time now.

Before I would dish out the kind of money Merc wants for it`s props. I would look at the Power Tech props half the cost and my 182 TS runs much better then any Merc prop I tried on it. I can PM the number, they have a great exchange policy even if it is months later as long as the prop is like new.

Check Dan’s prop shop online.

Thanks guys. Now I’ve got another problem….my thumb trim switch went out last week, so now I’m going to have to take that all apart and fix that before I can play with performance again. Joy. I’m going to put this on the shelf for now, but will pick it up again in the spring for sure. Guess I’ll have all winter to start more research now too. I’ll be calling on you guys again–thanks!

Quote:

---

Hey guys,
I’ve got an 18′ Crestliner Tournament Series boat with a 150 VMAX Yamaha. I’ve currently got a 19 pitch prop on, and I don’t remember what my max RPMs are, but my max speed is only 42. I tried my buddy Chris’ (sharkbait on IDO) 4 blade prop, and I believe it’s the same pitch or very close. Max speed is real close to the same, top RPMs were 4700.

So here are the questions. What does a 4 blade prop do for you that a 3 blade can’t/won’t? The only thing I know is that it’ll give you better handling in corners (I think), but that’s about it.

Also, how do I find out what the max prop is that this engine will push? Would I try going to a 21 to see how it does? Or more?

I’m mostly curious to see what kind of speed I can get out of this boat, and to make it the most efficient.

Propping is one thing I’ve never really been too good at, so I’m eager to learn more about this. Thanks–

---

I read all the post on this tread and your right with moving your motor up, but that prop you have on their now is way to much diameter. You need a max diameter of 14.5″ the prop we had good luck with your combo is the Powertech Ras3 19 pitch 3 blade which has a 14.25″ diameter. Thats the same prop TomP. is running it will perform very well on your boat. That 21m that you have is the salt water series which is usually is run on a heavier boat with a 4 stroke yamaha on the back.

Welcome to IDO Propman!

-J.

Thanks Propman, and welcome!

I appreciate your post. I’ve kinda given up on the deal until spring, then I’ll hit it hard again. I think moving the motor up was definitely the right thing to do, and now I think the right prop will make all the difference. The local shop said they’d let me take a few out and try em next year, so that’ll be a big help.

You’re saying that 4 blade I’ve got is a saltwater series prop? I know it came on Chris’ Yamaha that was a 250, I believe, so it was a bigger engine.

Thanks again, and now spring can’t come soon enough!

All right guys, the propping is back in focus for me after a much-too-long winter. The trim switch was a surprisingly easy fix, so we’re off and running.

To update the current situation: the prop I have is a Michigan Wheel 19″. I walked out of Buzz’s Marine in Kearney with a couple different props to try. They gave me a Mercury Vengeance 19″ and a Laser II 21″.

I was pleasantly surprised going from one 19 to another. The Vengeance is a nice prop, great grab and hole shot, and I instantly shot up another 3mph to just a bit over 45. RPMs went up to almost 54.

The Laser II did not pan out at all. Once you hit the throttle, it was instant cavitation. Hole shot virtually disappeared, and while I did gain another 1.5 mph up a bit over 46, it took a while to get there. The Laser has the vent holes, while the Vengeance does not. The vent holes were about half open. I wonder if the vent holes were completely shut in, would my cavitation problem disappear and my hole shot establish itself again?