I am having I think a ventilation problem with my new to me

[hotairgypsy]

So i finally got a good weekend out on the water to test everything and houston I have a problem. I will get over 3500 rpms and depending on water condition or where people are sitting i will hit what i call air pockets where the rpms will shoot up and boat slows down...i cannot go WOT without it happening. here are the simple facts

2001 20' LOWE pontoon boat
90HP Johnson outboard made 10/2000

prop on boat when i bought it used marked 1413 so i assume a 14" 13 pitch

was dinged up so i order a new one and was shipped a 13.75x13 and that is what is on the boat now

i know the diameter is .25 smaller but would this be enough to cause my issue...when the rpms shoot up they got to around 5500 but i yank it down right away as not to cause any damage. The engine is set at the lowest setting. I don't know if i should be considering a jack plate.

I did change some stuff up when i bought the boat which would change the weigh distribution. My boat had one large l shaped couch in the back, two small seats in the middle and two fishing swivel seats in the front. I installed two couches in the front...took out the middle seats and put a little smaller l shaped couch in the back...installed an awning in the front also for shade. I have taken the boat out with just myself and was able to get it to WOT but the trim is very touchy to keep it from blowing out as i call it. minute i get weight on it dif story.

so i need some direction if anyone has any ideas before i have to buy a crapload of props to solve this issue. thanks gang

engine.jpg (441.35 KiB) Viewed 3666 times

[HandymanHerb]

You have to keep all the weight to the back on smaller toons, I put a Prop Guard on mine and it helped with the blow out, really helps in low speed handling

http://www.propguardmarine.com/

[GregF]

That motor is plenty deep enough, in fact too deep based on the water line on the toons and motor foot.

Where is the cavitation plate vs the bottom of the motor skid plate?

The skid plate should be presenting a flat stream of water to the motor and the cavitation plate should be an inch or so below that plane.

[Ron Burgundy]

What Herb said. Gotta keep the weight in the back. Mine does the same thing. It's annoying. If you can get some furniture out of the front and into the stern to encourage people to sit back there it should help.

[dockholiday]

What Herb said. Gotta keep the weight in the back. Mine does the same thing. It's annoying. If you can get some furniture out of the front and into the stern to encourage people to sit back there it should help.

Yep almost everyone that gets on the boat want to sit as far forward as they can. I usually have to redistribute and make sure everyone has life vest within reach before taking off.
doc

[GregF]

Have you got a buddy who can shoot some video of your boat underway?
Try it with people up front and in the back. See if you can figure out how deep the motor is running

[badmoonrising]

I had a slight cavitation issue on my Party Cruiser, installed a Doel Fin and problem solved.

[hotairgypsy]

i am liking the idea of the prop guard for a few reasons...they are dropping the water a lot at the lake and new rocks are appearing constantly. this past weekend i was cruising at like 2 mph and hit one...got some nicks on the prop so this would help prevent that and could help with my problem...time to get searching and see if i have any luck

[ROLAND]

You have to keep all the weight to the back on smaller toons, I put a Prop Guard on mine and it helped with the blow out, really helps in low speed handling

http://www.propguardmarine.com/

Herb.. don't want to hijack this thread, but I wanted to ask you if the prop guard made that much difference in low speed handeling... dose it make the boat handle differently at higher rpm's.. in other words, con's and pro's of having a prop guard... lake levels dropping again, so I'm thinking about getting one... also might help in low rpm situations as far as handeling when loading the boat on the trailer...

[Drago]

You might find this an interesting read...
http://continuouswave.com/ubb/Forum1/HTML/004738.html

[badmoonrising]

Also note that if your motor is under warranty, make sure using a Doel Fin or similar product won't void your drive warranty. When my boat was repaired last year, the Mercruiser techs would not transfer my Doel Fin to the new drive and told me if I reinstall it, the drive warranty is void. So for now, I put up with occasional cavitation. Not like my boat is a speed demon anyway, and I can just send all those naked women to the stern...

[HandymanHerb]

You have to keep all the weight to the back on smaller toons, I put a Prop Guard on mine and it helped with the blow out, really helps in low speed handling

http://www.propguardmarine.com/

Herb.. don't want to hijack this thread, but I wanted to ask you if the prop guard made that much difference in low speed handeling... dose it make the boat handle differently at higher rpm's.. in other words, con's and pro's of having a prop guard... lake levels dropping again, so I'm thinking about getting one... also might help in low rpm situations as far as handeling when loading the boat on the trailer...

Makes a big difference in slow speed handling, if you get in low water you can tilt the engine up and it acts likes a jet drive to get you through it, safer if the kids love to swim around the tool, protects you prop from weeds to rocks.

6x6 hit a rock with his and broke it at speed, but the prop was safe, he was 8 miles from the house, on a day with no one on the lake to help, he replaced it, now in Florida we have the floating rocks, if your out at night, there called gators, one night coming back in from fishing almost back to the ramp, I made the turn into the channel and seen a 10 foot gator, didn't have the time to turn and neither did he.

He dove, but not fast enough, I hit him with a toon then he hit the engine hard, with the propguard we were both safe, he would have broke my prop.

Cons are you lose one MPH at top end

[JDB]

Simple answer is YES. that 1/4" you lost can make all the difference in the world !

[GregF]

Are you sure you are not just picking up leaves or grass?

[hotairgypsy]

i live in the desert...no leaves or grass at the lake. it is sand and rocks with dead bodies occasionally