Hitting rev limiter

[Apex]

I have a 2008 Suzuki 150 4-stroke on a 18ft. glass deep V boat. The motor hits rev limiter at WOT when trimmed up a very little bit. I started with a 19 pitch stainless prop. Then went to a 21 and 23 pitch and its still happening, but slightly getting better. So I am either going to get a 3 blade 27 pitch or a 4 blade 29 pitch (motor takes a 19-29 pitch prop) Just wondering if a 4 blade is going to increase my idle speed in gear and or decrease top end over a 3 blade?

[norma]

A four blade prop lifts the stern more so boats heavy in the stern ie bass boats will get on plane quicker. Try the 27" pitch next.

[CAMAN]

How close to redline are you before you start adjusting trim? If you're at a good/safe rpm and its just breaking loose and over-reving at just the slightest of trim adjustments it sounds more like cavitation to me and the motor is mounted too high.

But if you're already close to redline at holeshot and you go to adjust the trim to improve the ride, yeah it will redline no matter what. But going from a 19 to 23 in that case should have seen a fairly dramatic improvement, unless it was way underpitched to begin with. Which it sounds like it may have been.

Is your holeshot still good or is it starting to struggle getting up?

Before you just start throwing props at it I would make sure and know exactly what the problem is. If you go from a 19 to a 27, that will either kill your holeshot, or you have some magical powers and physics dont apply to you, because I've never heard of a boat/motor combo that was able to run that wide of a range of pitch and something not get hurt in the process.

But IMO, for what sounds like a fairly heavy boat, a 23 pitch on a 150 sounds about right. Maybe going up to a 25 if you aren't having any issues with holeshot.

[hydro]

What RPM are you running when the motor is "on the limiter"? Is there a possible electrical issue causing this? That should be looked at first.

Since you have already dramatically increased the pitch and the problem seems to have changed little, I doubt the prop is the culprit. The first thing to check, is as CAMAN suggested, the motor height. To do this, place a long straightedge on the lowest point of the hull and measure the distance from the hull to the centerline of the prop shaft. That is your starting point. If the measurement is 3 ½” or less I bet that’s the problem.

Do you have a jack plate? If so just lower it ½” at a time and re-test to see if the problem gets better. With your combo I would start with the prop shaft about 4 ½” down and adjust from there. Go too deep and it will be sluggish and torque steer, too high and it will get loose and blow out. I would try the 21” prop to start considering your combination. If lowering the motor seems better, check the holeshot and high speed turns for blowout or the prop losing its bite on the water, both signs of running too high.

Don’t waste time and money on a 27” or worse yet a 29” 4 blade prop. Both are way more prop than your 150 HP motor will spin that on your boat.

[boatfixer]

I agree, check the engine height to make sure that isnt the problem first. Using a straight edge, check to see if the anti-ventilation plate is level (or very close) with the lowest part of the hull, unless you are using a surfacing type prop, which I doubt you are.

You also didn't mention the actual RPM. Its possible there is a problem with the ECU.

Has it been like this from day one?

[Black_Bay]

Check the engine height first. If that is OK I'd look for a 4 blade prop, like a Mercury Rev 4 in a 23 to 25 pitch. Suzukis have deep gears and are able to turn larger pitch props. A 4 blade prop in 29 pitch won't get you in your optimum RPM range.

[hydro]

What type of boat do you have, and any idea what it weighs? Hull design and weight can play a big factor. And as mentioned above, those are really deep gears!

Out of curiosity I looked up a 2010 Suzuki DF150 and it has an rpm range of 5000-6000, with a gear ratio of 2.5:1. If we assume a 6000 rpm and a slip number of 15% for the sake of calculation, your theoretical top end speeds should be about:

23” pitch 44 MPH

25” pitch 48 MPH

27” pitch 52 MPH

29” pitch 56 MPH

I can see why you were on the limiter with a 19” prop, but the 23” should have pulled without too much over rev.

[Apex]

No jack plate. Not cavitation, only does it at WOT. No compromised hole shot, nor do I care about it. The motor can only be dropped another inch. I have talked to the dealer and suzuki about the issue and they say the prop for sure. Hydro petty much nailed it on the nose. Its Triton 177 walleye boat weighing apx. 2,000 lb. w/o motors so about 2600 w/ fuel and gear. 49mph with a 19 51mph with a 21 and 53mph w/ a 23 pitch. As far as rpm's its getting up to 6200-6300 when it hits and limiter m is set to around 6,100, which would make sense about the 15% threshold. So w/ all the info 3 blade 27??

[hydro]

I would not make the jump all the way from 23" to 27". That's a huge change and once you get close to the combination's sweet spot, a small pitch change will make a big difference. Once you start looking at pitch of 27" or more, the selection starts to become limited to designs for high speed running.

Since you fave a fairly heavy boat that was designed primarily for smooth ride and rough water, I would concentrate on matching the prop to the application. Look for a 4 blade in the 25" or 26" range designed to carry a heavier boat. The extra blade will provide more thrust, loading the motor and reducing rpm at the same pitch. Also, back to your original question, with more pitch you move faster at idle and handling will become difficult. You wind up shifting in and out of gear a lot while maneuvering to the trailer or dock, and forget trolling altogether.