Trying to the right prop!

[Chris]

Ok guys and dolls, I need a little assistance.

As most of you probably already know, I have a 1992, 170 Pulse B/R, with a 1991 Mercury XR4 150 HP motor. The boat currently runs a high five, 22" pitch prop and it will turn its maximum RPM of 5800 and I get about 58-60 MPH. I don't have a bow cover.

I'm going to try to pick up a used Mercury Laser II prop on Ebay. So I was wondering if I could get some suggestions on what Pitch, I should get. If anyone else has run the same set up and had luck with a particular prop, I'd love to hear from you. I'm trying to find a prop which is for top speed as I already have the high five for skiing and tubing.

Also, I believe I have the smaller gearcase, but could someone tell me how to positively identify if I do or not. I gather I can measure it somehow? And also what is the best way to determine the current "exact" diameter of the high five? It seems to measure about 14 inches.

Thanks!

 

[Eriktheviking]

Chris,I have a Merc. prop brochure from 1994 and the only 22" High Five prop they list is a 13" Diameter.

 

[Chris]

Originally posted by Eriktheviking61:
Chris,I have a Merc. prop brochure from 1994 and the only 22" High Five prop they list is a 13" Diameter.

It could be Erik. It actually may not even be a merc prop. It doesn't have the high five stamping, so who knows. It does have five blades though!

 

[Mark]

Chris
Measure the hub. Large is 4.75", small is 4.25". If you get the wrong size it will not fit your motor.
I tried a 20" and a 22" laser on my Diplomat with 130 Yamaha and this is what I discouvered. On take off the bow went straight up until it got on plane, of course making it less than ideal for skiing. The 20" made 57mph @ 5800rpm and the 22" 57"mph @ 5400rpm. It seemed to me that as I trimmed the motor out I got major bow lift and steering torque with no increase in top end. The thing they did do very well was great mid range cruising speed. However, on balance I could see no advantage over my standard 21' Yamaha SS that was doing 60mph @ 6000 rpm and still had great hole shot and no steering torque. Incidently I tried my 19" Ballistic off my previous motor (115 Merc) and it did 57mph @ 6000 with no trim. If I had trimmed it out, I would have over-revved. I know this seems mathematically impossible for 19' pitch but the Ballistics make great speed. I am planning on swapping this prop so I too am interested in suggestions from the experts. Anybody have experience with the Trophy or Yamaha 4 blade and what pitch would you recommend for Chris or myself?

 

[JW]

On my 1992 Pulse 171 with a 1992 XR6 (2.5) I was able to spin a 26" Laser II for best top speed and rpms. The only time I had trouble was when it got really hot and muggy, then I'd be down to 5300 rpms. I had the small gear case, all the XR motors have the small case unless it was blown up and replaced with the large case. The 24" was probably best for all around use, but would hit 6,000 rpms at best trim/speed so it was a little small.
With the little gear case, you'll be looking at the 'even' number pitch props. Odd pitch numbered props are for the standard gear case.
For your smaller motor, you'll probably have a 24" Laser II for best top speed. Put that motor on a jack plate and then you can play with engine heights. 24" for top speeds, 22" for all around use. You won't believe the bow lift and top speed of that Laser II compared to the High 5.

 

[JW]

P.S., not ALL of the XR motors had the smaller gear case. You could order the motor either way, don't want to confuse anyone with my previous post. On top of that, the new XR6 Classic motors do not offer the small gear case. You can only get the late model XR6 with the larger cases. Best to measure the prop hub as mentioned earlier..........

 

[Chris]

Thanks fellas.

When you measure the prop hub....from exactly where to where am I measuring?

If I pull the prop off and measure the back, would that give me the proper measurement?

 

[JW]

The diameter is actually the diameter of the case. If your propshaft was removed it would be easy to measure it. Or use a big caliper. Even pitch Laser II and Trophy (and probably all of Merc's props?) are small diameter, odd pitch props are larger diameter. Since you have a 22" High V prop, then you have the smaller diameter if it fits tight and you have the larger case if you have a small air gap around the leading edge of the hub.

 

[Chris]

I will measure it next weekend.

Thanks JW.

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Checkmate-Boats.com-The Fanatics Home!

 

[Mark]

JW
You never gave us the numbers you were running on the Pulse. What top-end at what RPM? A 26" Laser, even a 24", is a lot of prop for a 150 hp Merc.

 

[JW]

Full background: My 1992 Pulse 171 was the first year for that hull, and the 1992 XR6 was the first year for that motor. There were larger Pulse models introduced earlier, but the 171/170 was the last 'new' Pulse model, introduced in 1992. Late 1991 the XR4 turned into the XR6 for the 1992 model year when it increased from a 2.4 to a 2.5 block. There were higher horsepower motors in the 2.5 block introduced earlier, the 150 hp version was added that year. So we had a 'double firsts' boat/motor combo. It was tuned for a LOT of torque, and had an rpm range of 5400 - 5800. That's why I could spin a 26" prop. The XR6 gearcase (as it was called back then) was the smaller diameter case, with 1.78:1 gearing as opposed to the standard 1.87:1 gearing. That means the prop turns a little faster per a given engine rpm. It went through the water a little easier also because of the smaller diameter. It also breaks easier because it's smaller. This gearcase was really designed for smaller and faster hulls than Checkmate was building, but we were able to take advantage of it anyway. It had lower water intake holes than the standard case, so I could run it higher. With 6" of setback on my closed bow 17' boat and a 26" Laser II, I was able to run 70 mph at approx. 5500 rpms. I could have used another 6-8" of setback but these were the beginning days of my high performance boating. It was a handful to drive at that speed too. I would NOT turn a novice loose with my old boat. My current boat (Pulsare/Promax) is such a superior design that I can turn a novice loose and let them run 70+ mph without fear of losing control. I miss my old black Checkmate with that XR6 though..............

 

[Chris]

Hey JW. I found this website that lists Merc RPM ranges. It listed the XR4 as 5400-5800 and the XR6 at 5000-5600.

Here is a link.

RPM Ranges

 

[Chris]

Does that seem right for the XR6?

I personally try not to run mine over 5400-5500.

 

[JW]

Don't worry about 'hurting' the V6 Mercs by running them a little past the rpm range. The rpm range is a 'power tuned' range rather than a 'blow it up' range. The 150 has ports/exhaust tuner/carb jetting that create the best horsepower in that range. If you want to get to your boat's best top speed, use a larger prop that hits the lower end of the power band, somewhere around 5400 rpms. To get much better acceleration but with slightly reduced top speed, prop it to reach 5800 - 6000 rpm. My 24" Laser II on the Pulse would allow the engine to hit 6000 rpms. My 26" would allow it to hit 5500 rpms. The 26" was faster on top end, but struggled out of the hole if I tried to pull up a big skier.
One advantage of buying bigger: If you find a minty mint 26" Laser II prop and it only allows your engine to hit very low 5k range, you can easily have it 'worked' by a known good shop to increase your engine rpms. It's easier to start big and work down than to try to make a small prop work bigger. Take a stock 26" Laser II and have it thinned and balanced and you'll have a race prop. My 23" Tempest has been thinned and it works wonders on the back of my Pulsare/Promax. If you're the type of person that keeps your prop safe, you can thin a prop for better performance and it'll last a long time. My prop is at least 8 years old and I surface it and it's still in excellent shape.

1995 Pulsare 2100BR/1995 Mercury Promax 225 2.5 EFI/ 1.87:1 Torquemaster/ RapidJack Heavy-Duty manual 10.5" setback/ 23" Tempest worked for ski duty

 

[JW]

You may want to look at other than Ebay for a prop too. Check the prop section of Scream and Fly. Also check the back pages of Family and Performance Boating and Hot Boat. There's a couple places that sells brand new Laser II props for around $350 USD.

 

[175checkmate]

I agree, try a laser, I love that prop. I turn mine about 6000-6200 depending on weather. I need to add a pad. I can still run 65 mph with a boat load of people and fuel of fuel. Pulling up a skier is no trouble at all. Infact you can't use wide open throttle on take off, if you do the guy on the ski's will leave them behind.

1975 Checkmate Tri-mate 2, 2.4 200+ / Sky jacker 6" plate / 25p Laser 2 prop

 

[Mark]

This discussion has left me wondering about jackplates. What do they do in terms of holeshot for skiing? I know Chris pulls skiers and so do I. What kind of setback for these short Mates? There's not a lot of distance at the steering cable either, can it make the bend? Bill, what was your experience on the Diplomat?

 

[Shameless]

Mark,
The Jack plate mad a huge differance all ove the spectum. It really made that boat come alive. I spun a 24 Raker whick is a huge prop for a little V-4. It planed in about 3 seconds. When I would run the 22 Raker I had, It would literally jump out of the water if you hammered it. I would not even have to tuck the motor all the way under for it to pop up on plane. Tha Jack plate gives you so much versatility. My only regret when I put my plate on was I did not get the hydraulic plate so I caould adjust it on the fly. I picked up on average, 10 mph, depending on how I had it set for the day.

 

[175checkmate]

I agree with Bill, a jackplat emake a world of differance. When I had the hyd. plate the differance between all the way down and all the way up was 18 mph. The old plate was worn out and did not have any setback. The new plate is manual and has 6 inches of set back.
I also mounted the plate alot higher on the new transom.

1975 Checkmate Tri-mate 2, 2.4 200+ / Sky jacker 6" plate / 25p Laser 2 prop