HELP, Suddenly losing momentum when under power

[g8tors09]

Hey everyone,

Here's what's up! I have a 2yr old 26ft Southbay made toon. Bought it new! I have (only) a 90hp honda with their extended foot. EVERY single time I take her out we have a problem. When we are cruising under power no matter the wave conditions we have at least one occasion of losing momentum. Only while cruising, everything is fine and then BAM we suddenly stop going forward, the engine rev's up and nothing. It is almost like we are hitting the beach. Now when I lower the power down we get back going. This is an everytime event. I have taken it to the dealer and of course " it doesn't do it for them" The hub is not stripped. They are currently taking the prop to make sure it has the right pitch. I beleive it is a 14in which from what I have checked is the proper size. It is quite a pain because everyone is being thrown forward when it happens. The engine is down as low as it can be without hacking into the transom. Not sure if it is Cavitating or not. They have checked out the engine and have found nothing wrong there. I really beleive them on that but any suggestions????

[GregF]

You can mark the hub and the prop with a sharpie pen to be sure it is not spinning but it really sounds like you are just cavitating. There are a couple of "prop" threads here talking about that.

Are you picking up grass or leaves? That will do it.

[g8tors09]

No grass or leaves. I am in the salty bay! I will try the marks when I get it back this time! Thanks for the tip.

[jrolin1]

I agree that it sounds like you are cavitating. Try trimming it down as far as it will go and see if it helps. You may have to lower the engine a hole or two.

[GregF]

Another issue is how are you loading the boat? If you have everyone up front, as people tend to do, you can be bouncing the prop out of the water.

I see that a lot watching other pontooners.

[g8tors09]

Engine is already as low as it can be without cutting into the transom.

[g8tors09]

possible but I have tried many trim settings and configurations. However almost everytime the majority of the people are upfront.

Someone mentioned an attachment to the foot almost like fins for planeing. Anybody heard of that working.
Thanks

[rrhodes]

Why do you have the majority of the people up front? Uneven distribution like that will cause the rear of the boat to sit higher and could contribute to your problem. When underway you should keep the majority of the weight closer to the stern.

[BobL]

My bet (assuming your hub is not striped) is prop blowout. You mentioned that you have had the boat for 2 years. Has it always done this or did it just start happening? Can't take credit for the following (robbed it from the internet) but it may help:

****************
1. Gearcase inconsistencies: If you have a gearcase that has been run up on the rocks a few too many times, or has a nosecone that has epoxy popping out of it or a skeg that is only half there, the gearcase cannot provide the proper rudder effect, thereby allowing the gearcase to "crab" or slide sideways through the water too much, creating a vacuum or air pocket in which the propeller tries to operate - unsuccessfully. Solution: Be sure to clean up all the nicks and gouges in the gearcase. Also, be sure the nosecone is put on straight.

2: Motor is too high: If the motor is too high, the prop will not be able to lift the bow, causing the drive to use too much trim causing the propeller to be angled downward, thus causing the force itself to go sideways through the water - unsuccessfully. Solution: Be sure to use the proper engine height.

3. Hull Design: Certain brands of boats are more prone to blowout than others, based on their hull designs and dictate more care be taken in the setup stage. Solution: Be sure to have a competent, knowledgeable, experienced person rig your boat.

4. Speed: When you go too fast with a stock gearcase, the water hits the front of the blunt bullet and actually "bounces" around the prop. Solution: Add a nosecone to improve the hydrodynamics of the gearcase.

The problems are typically a combination of these issues. Gearcase modifications and prop changes can drastically reduce your chances of blowout, but when you go fast it becomes part of the nature of the beast, so to speak. Typically a blowout is immediately preceded by a "loose" steering feeling, an increase in RPM with no speed increase, and sort of a drop of the nose. What happens after than can best be described as "WHAT THE HECK WAS THAT?"

[g8tors09]

Just the fam likes riding up front. I will redistribute next trip. According to the dealer, and I pretty much trust them, no stripping has occured on my boat. (ain't that the truth) Yes it has done that since DAY 1 and the boat and engine have never been in the water without me.

[rrhodes]

If you have ever been out by yourself or even with one person up front and it still does it then weight distribution won't help however loading the rear heavy would help you get the motor deeper in the water. If it still happens then I would ask the dealer to take a ride with you.

[lakerunner696]

You trust your dealer but he hasn't mentioned it might be cavitating?

Remember your the captain so be firm if necessary to level the load.

[2875RLXIO]

It sounds like cavitation to me, but you should see a spike in RPM's as it happens. Try running a different prop (maybe a little less pitch) and see if it goes away. You can also get into changing the cup on the prop, but I would just try a different pitch first to see if that is the problem. Over trimming can also cause prop cavitation.

[badmoonrising]

It sounds like cavitation to me

I agree..try a Doel Fin if the boat is loaded correctly. When my Party Cruiser was new I had a problem with cavitation and the Doel Fin solved it.

[WaltF]

Agreed.. cavitating.