another prop question... 4 blade help me?

[jbanderson]

Ok I have mounted a 150 marinier 2.5 efi inplace of my blow 75hp mariner.
I cannot get a good bite on the prop, I tried the best thing I could find at the marina witch was a 17pitch solas 14.8" diameter.. It hooked as long as I had the trim all the way down witch is not good at all. As soon as I tried to pull the boat out of the water with the trim it would vent the prop.
So.. It seems to me from what ive been reading that pontoons are bad about venting the prop, so wouldnt a 4 blade be best as long as you had extra power to turn it? (witch I have planty of)
I need to get this thing hooking up!! Please help!!
thanks

[texaspontoon]

It may have something to do with the engine height. Do you have any holes you can go down lower with? Yes normally a 4 blade gets better bite less slip, but is not as fast.

I have a 15" x 14 pitch (custom made) but I am going to try three new props tomorrow including a 4 blade and a 14.5" x 18. I will let you know my results.

I am hoping to go up in speed when I have a light load.

[jbanderson]

motor is all the way down and I would have have to get foot extension to make the prop any lower, its a 20" motor just like the one I took off.
Im not worried about losing speed going to a 4 blade, no way I will ever get to use all the power of this motor I swapped on anyways.
I guess I should try a 4 blade. I cant get the toons out of the water AT ALL, it will run through the water like a plow cause I cant trim up without the prop slipping and loosing ALL bite.
Thanks

[tkrein]

another thing to try is a hydro foil might help. you might have to get a jack plate two things this will help it will set the motor back farther try and get some less turbulent water and should let you lower the motor farther check out some old posts about jack plates someone on here had to do it I dont remember who but it is there they had to turn the jack plat upside down to get the motor far enough in the water. good luck

[Bamby]

another thing to try is a hydro foil might help.

On one pontoon boat I owned I did actually install a hydro foil and it seemingly did correct or help the problem. But I latter learned more and found that when we purchased the boat new it actually wasn't actually rigged right from the dealer. I raised the motor a couple of holes (20 in. shaft also) and truly corrected the problem.

It may have something to do with the engine height.

It may have everything to do with the engine height. I've had the best results when the anti-ventilation plate (white line) is more or less level with the transom. This is also a 20 in. shaft motor and notice that it is also raised a bit (yellow arrow) to achieve the proper height. Now take note to the left of the white arrow, if your motor is also anti water dynamic like this one with any factors that are disruptive to water flow. The boils created by such may be the real source of your problem. Deeper is not always better, there is a chance that you may actually need to raise it some to correct the real problem.

Motor_Hgt.jpg (132.73 KiB) Viewed 4109 times

[texaspontoon]

One last theory....when I pull heavy loads on my boat (pulling double tubes with 8 riders total) I start to cavitate with even the slightest raise of the trim. Are you having problems with this when you have a heavy load of people? If you have enough clearence, try going to a 3 or 4 blade 15" diameter x 15 pitch prop. (if you have the clearence around your cavitation plate).

Good luck getting it dialed in, and be sure to tell us what it was. I agree with others about the jack plate and engine height, but jack plates are VERY expensive. Try the prop first. West Marine will let you return them within a few days of purchase if they don't work out.

[Bryden24shp]

I think you need to post a picture of the set-up, from the rear and side views of the boat. Really need to see where the engine height is in conjunction with the pontoons. Otherwise we are just guessing at best. I thought that Solas would be a good choice. What kind of rpm's are you running out of the hole?

[jbanderson]

tach doesnt work but not many rpms, will be fixing that asap.
Boat is in the water and is a big hassle to move but prop is about 4" below toons

[Bmac]

Does sound like the motor is too high,or there's water in your front compartments? Thought mine were dry up front when I bought it,but syphened a lot out of them.

Some four blades will run a lil higher at speed,but your also going to get more sternlift from most of them. Not what your looking for yet. If you can't trim a 3 blade out a 4 blade probably won't help much. It may be the same height as the 75 hp,but your prop is a bigger dia. now. Closer to the surface,and your trying to suck more water through it faster with the higher pitch.

If the tubes are dry. Try taking a few friends out next time. If it's worse with them sitting up front ,and better with them setting in back then the motor needs to drop. You might be able to find a manual setback plate for a decent price. Mount it upsidedown as mentioned before.

[Bryden24shp]

tach doesnt work but not many rpms,

Really, that puts a different twist on things. Ya, Bmac may have something there. Sounds like something is wrong with the boat or the motor. Ya, fix that tach before you do anything else. You need to gauge the rpm's before any propping can be done. Is that a new or used outboard?

[jbanderson]

its used, Only thing I noticed with setting the motor back is that I will have to buy longer steering cables and the controls wont reach any further either... that will be a BIG exspense.
Toons had a leak on one side but we drained them and patched the holes.

[GregF]

Ref the cables I got them cheaper at the dealer than West Marine and they were real cables, not a kit of parts that almost works.

[Bryden24shp]

I am gonna ask a stupid question, here. I am sure you looked, but, you never know... There are trim limiting switches and pin settings on some outboards, that will limit trim travel, in and out. Are you adjusted all the way down? Just an idea that popped into my drained brain as I was waxing my truck.

[jbanderson]

yep, any thought counts lol but There is no limit on the trim, it goes all the way

Im just going to have to decide that the hull is not designed to run any faster than say 15mph.. I know when I used to ride on it with the 75hp it went faster, probly closer to 20 and would get the logs out of the water more than they do now, Its crazy. no marina or any boat mechnic can suggest anything. Nobody has ever had this problem before it seems.

[GregF]

I agree with the people who think this is just churning water hitting the prop. Is there a flat skid plate on the bottom of your motor bracket?
Mine is a wide flat plane and I have never had a blow out problem running straight even though my motor is 4" above stock with the 20" shaft. The motor is presented with a flat plane of water.
The idea of actually looking between the pontoons while you are running is good but because of the danger a camera shot may be safer.

Watch those incoming wakes. If you fall in, the only way out is through the prop.