Ventilation Issues...

Hey fellas. Trying to find a solution for what appears to be a ventilation issue. I have a 14' SeaEagle with a new / used '97 25hp 2 stroke Merc. There's plenty of juice to get up on plane but the prop loses bite when trying to get more out of it (forget hard turns with throttle open). We were looking at it and it seems that the water is alot lower in the box than outside of the tubes. Seems like the prop should be lower (especially on plane). Transom is approx 15.5" and vent/cav plate is approx 16.5-17". This should be a fun boat to squirt around on MT lakes and rivers but something isn't quite right. I'm reluctant to cut down the transom and don't want the prop any more exposed / lower than it needs to be. Anyone else have this issue or heard something about it? Does a larger vent plate help? Different prop? (standad 3 blade / 13" pitch right now).

Thanks for any help, Andy.

Re: Ventilation Issues...

I just replaced a prop on my 25HP using the following chart from Mercury. I went with the 9.50 pitch for more power. I suppose there could be unseen/unknown damage to your prop causing the problem. When you run in a straight line are you hearing the prop trying to get a bite? When I turn corners I can hear the prop not getting a good bite.

There are others on this forum more knowlegabe that will hopefully respond to the correct transom height.

Re: Ventilation Issues...

Welcome to the forums,

Inflate well sib tubes and keel, with boat at floating/resting postion trim engine to be perpendicular to surface, place one adult passenger at bow, go for a wot spin, does it betters ? If so, you were badly trimed. If boat is well ballanced and correctly trimed as in pictures and experimenting excesive water splashes or aireation, ventilation, you have an engine height issue which has nothing to do with ballance or trim angle.

Happy Boating

Re: Ventilation Issues...

Thanks guys. Have the day off and plus 90 degree temps so will likely find some water. Sea Rider-I'll try different motor trim positions today but it seems the deeper / more perpendicular I can drop the prop (while on plane) the better the bite. I don't seem to have much issue getting to plane even by myself (good bite with the stern deep pre-plane). Pack Rat- Thanks for the chart. I need a back-up prop for this setup anyway so will see if I can improve. What do you think about a 4 blade? I have plenty of juice with this boat / motor combo.

Thanks again, fellas. Carpe diem!

Re: Ventilation Issues...

Did you test as recommended ? if so, how did it went ? 4 blade props are for moving more heavy boats that drags more on water, pontoon type boats not sibs/ribs, don't need them. Go for a wot test with you alone and gear and check max rpm achieved for that combo. Will need to install an induction tach (Tiny Tach) to check, just inflate well the beast.

Happy Boating

Re: Ventilation Issues...

Hey Sea Rider!

Sorry so long to get back. Tried what you suggested with no joy. Talked to a local, long-time marine engine tech and he thought a 4 blade prop would definitely improve the issue. I purchased a 4 blade Solas 10.2"D x 12"P and a Tiny Tach and went for a spin. Much Better!!! Ventilation almost nil. Turns are still a vent problem and I have to feather throttle at other times but... with just myself (170lbs) and a 50lb dog I was able to achieve 5350rpm at WOT. My 25 Merc has a recommended WOT range of 5000-6000rpm. I have another 4 blade coming with a pitch of 11". I think I'll need the increased RPMs with another person and/or dog in the boat.

I'll post with new results when I get on the water again. My Griff just had a litter of 8 so I'm FUBAR for fun for awhile

Thanks for your input... stay safe, ab...

Re: Ventilation Issues...

If you still have ventillation, aireations issues at close tight turns you have a transom engine height issue, go for a wot spin with adult sitting up front at bow area and check your water flow as in the example.

http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be Determine if flow is passing under small upper plate which is the sweet spot, middle space between small upper plate and lower AC plate, or near lower AC plate ?

With correct transom height a standard 3 blade prop should work with no problem at all at speed on straight line courses or at close turns and even under chopy seas conditions.

Happy Boating