just repowered - need prop help - current ventilation

[rondolg]

Good Morning-

I just repowered my 2010 Encore Prestige 25ft pontoon. I went from a Mercury 60 outboard to a new Mercury 150 outboard. The problem I'm having is ventilation at 4k rpms. As I try to full throttle up the rpms will jump from 4k to 5k+, the boat feels like it just stopped in the water.

The new prop that came with the new motor is a 15 X 15 Mercury Enertia.

The hole shot seems just fine and there is plenty of power to move the pontoon along. I've included some pics of the new motor setup on the pontoon. The pontoons do have lifting strakes also.

Any advice would be welcomed. The boat is mostly used for transporting 6-10 people out to the nearby island to hangout, so is mostly loaded down.

Thanks very much,
Ron.

 

[Scott Danforth]

where is the AV plate compared to the water line when your under way?

 

[Sea Rider]

If current prop is doing its homework right could have the following issues or a cocktail of them :

1-Deck load badly distubuted
2-Engine badly trimmed
3-Engine/Transom height with a mismatch

To cure that issue test as followa :

Run a wot test as loaded on calm flat no wind water cond, with engine trimmed to 90° and deck weight evenly distributed. Once toon it's on its way, pull head out middle transom and check at which lower leg is water flow passing by right under middle hull.

If found passing too close to lower AV plate engine will experience excessive prop aeration worse on non cal flat no wind water cond. Must sit engine much higher on transom for water flow to skim right unde upper small plate, prop will achieve its best thrust as there is a higher water bed for top blade bite, grip, etc.

Report what was found to go from there...

Happy Boating

 

[NYBo]

The motor looks like it's mounted rather high.

What is the HP rating of the boat?

 

[ahicks]

It sounds to me like the lifting strakes are doing a good job (too good at this point). By time the boat has accelerated to the point the engine is turning up 4k, they've lifted the boat (and engine) so high the prop is loosing it's grip on the water. I'm with NYBo here. The engine is very likely mounted (way) too high.

Would love to hear the results when you get it sorted out. I think that boat is going to fly!

 

[Sea Rider]

A visual inspection showing any engine sitting supposedly low, very low, high or very high doesn't matter at all. Once hull has achieved full hydrodynamic lift ( tech term for hole shot) it's a different story. Only a wot test on flat calm water cond will show what needs to be done to correct any lower leg producing back transom water splashes or prop aeration in any form whatsoever.

In reality need to match the hardened water flow flowing under middle aft hull whichever flat, round, shallow, deep V shape it has against lower leg, if dialed right under upper small water deflector plate much better, that spot achieves the best prop thrust specially for under powered engines powering most boats, pushing heavy boats, toons and if wanting to squeeze the max out of any HP engine along a spot on prop maximization.

Was wondering why this basic ABC boating tech informationt it's so complicated to understand, boaters should take advantage of this information and experiment by themselves, won't find it written in any Boat/Engine Owner's Manual as parties don't want to be stabbing and blaming each other for transom and lower leg proven height differences between both for combo to achieve a perfect match. The consensus is : Let final boat owner blow his head off and resolve these unwanted factory issues best as he can.

Happy Boating

 

[Faztbullet]

Was wondering why this basic ABC boating tech informationt it's so complicated to understand, boaters should take advantage of this information and experiment by themselves, won't find it written in any Boat/Engine Owner's Manual

Its in the service manuals. as has a chart to show mounting heights..

 

[jimmbo]

Pontoon boats appear to be a different breed when it comes to engine height. Maybe it’s the way water behaves when being channeled between the tubes versus sn conventional planing hull. Perhaps Pontoons should have hydraulic Jack Plates as standard equipment.

 

[Sea Rider]

Its in the service manuals. as has a chart to show mounting heights..

NOPE, it's same info stated on different brand Owner's Manuals, only states different AV plates heights for each brand motor which varies between 10 to 30 mm heights and none of them states any installation being even with rear middle hull. This is a repeatedly fallacy of this forum that seems will go on forever.

The chart is useless as no OB manufacturer takes into account that all boats transoms have different heights doesn't matter if all are say S ones which could vary between 38 to 40 CM in height to state a proven found example. One story is a dry installation (sitting any engine on transom whatever its height is ) a different story when combo is out of the hole at full plane.

As we haven't agreed about which is the best lower leg height for top water performance as you guys like having water flows passing around AV plate and I right under Upper Plate, let each boater test fully both height settings and check which one performs top for their application.

The sweet engine/transom height match is fine tuning any boat to get the max thrust out of their respective outboards along a spot on prop maximization. If you don't want, like or find that's too much hassle experimenting it, can keep boating as you have been doing so far and voilá.

Happy Boating

 

[Faztbullet]

You need to look at a Mercury service manual as it does address the issues you stated. Rubber duck set ups are different than performance hulls. If I set my engine/boat up and propped/trimmed it per your suggestions it would be running a 24 pitch prop and maybe running 60mph...but I run the AV plate 6" above pad and turn a 28pitch 5800 rpm 73 MPH GPS

 

[ahicks]

Faztbullet,
Regarding anything usable that Merc has to say about engine heights on pontoon boats, I'd have to see separate listings for a std. twin tube (w/different heights for large and small diameter tubes), same boat with lifting strakes, and tri toons, with and without lifting strakes. At that point they may have something usable, as each of these variations are going to demand the engine be installed at a different height. I have a hard time believing they've gone to that trouble and published the results....