Propulsion issues

[jlwardn]

This is my first pontoon and I have already had great help with a couple of questions. I went on my third cruise and noticed something that seemed bad.
I have a 24 ft partybarge and a 50hp engnine. I was going downstream and cruising 12mph at maybe 60% throttle with no issues. After an hour we did a return trip up river. Not a strong current river and it is large and deep. I noticed that any speed above 12mph the prop seemed to cavi or lose propulsion. It would act the same as if I trimmed up the engine and it was not in the water fully. It was trimmed down. It would also do this same exact thing if I turned the wheel/motor in either direction. I looked to make sure nothing was dragging from the boat/motor or prop. When going 12mph or higher I did notice that water seemed more pushed away from the prop(not sure how to describe it)....less water in front of motor surrounding it???? Motor is for sure mounted deep enough in water and it only seems like it is an issue and 12mph or higher. On my 2nd trip I had 10 people and it seemed to do the same thing. I just figured it was because I had ten people and they were sitting mid boat and up front pushing the front end of the boat in the water too much. Not that it has done it with me and my wife....all weight in the back. I don't know what to think. I explained it to my neighbor and he was quick to tell me that I need to add "fin" to my motor and it will help keep enough water over the prop so it does not cavitate. He is not always the most experienced person so I usually have to double check his advise.....he is batting 50% usually. If you guys have any insight....I would love the help.

[MH Hawker]

thats called cavation, its when the prop loses its grip in the water, and it can be caused for several reasons, motor to high, wrong prop, how the boat is loaded, and so on, it low speeds it may be a spun hub, that is one of the first things to test ( its free ), you do that by marking a line on the prop hub then using the boat, and once back on the trailer look to see if the mark is still lined up

[NonHyphenAmerican]

MH has a good idea.

Was fishing once and a guy asks if I can tow him back to the ramp.

Seems his hub had spun and the prop dropped off.

Towed him back and told him no when he asked to pay me.

I figure I'll be the guy stuck sometime and I hope someone helps me out.

[MH Hawker]

i was out last night fishing and while on the way to one of my spots a ran across a young husband and wife with 2 small kids and he was having starter problems and needed a 4 foot piece of rope to use to pull start and i happened to have some and it got him going, i asked if he wanted a tow back to the ramp and he said no not just yet, and he was running so i went on my way