pontoon performance question

[r&s20]

looking for your input, to start with i have a '94 smokercraft 20' fish and cruise type pontoon boat with a '88 90 hp omc motor. 23" toons no strakes ( i wish). i had a 14x10 power tech stainless prop on the boat but allowed motor to over rev.(4500-5500 rpm)and randomly ventilate even when below rpm range. so i lowered motor all the way and built a larger anti-ventilation plate. (later found one on line similar to what i built called a doel-fin). mine doesn't appear to be as long as thiers.any way since then motor was to low.have raised motor after every trip to lake am at top hole and at WOT still appears to low do ya'll think installing a jack plate would be worth the effort and cost.i think i could go back 6" with out new shift and throttle cables,steering cables.i am currently running a 13 3/4x13 aluminum prop.top speed is 25.5 avg is 25 (gps). not looking for speed really-looking for efficiency these old omc's are gas hogs.know what i mean. sorry long post but trying to get in all info.thoughts on this please

[Bamaman]

25 mph is about all you could expect out of 90 hp. If you're not experiencing ventilation, just accept your boat as it is.

They've all got their limitations.

[r&s20]

bamaman, thanks for the reply.but the reason i asked is not really for more speed,in truth we really cruise at 14-16 mph.we find that going over 20 mph it's hard to talk to each other.i go over 20 when i don't want to hear to boss lol.every time i have raised motor i gain 200-300 rpm.if i put a jack plate and go higher with motor i may be able to use a prop with more pitch and cruise at lower rpm using less fuel.is it worth it?

[tuned]

I have used manual jack plates on and off for years with pretty good success, including on my last pontoon. Not sure if you will gain anything or not, but if you don't mind the investment and the wrenching, give it a try. At worst, you end up with a plate you can resell. You have thought it through about the cables. THAT is where the real expense lies because you can't really resell anything there, plus the added hassle of changing them out.
If you have a cherry picker and don't even unhook your cables, you should be able to do a bolt job in a couple of hours without too much trouble. A six inch setback generally is a bit of a plus as well.
Before proceeding, you might want to verify that you can go up with the cavitation plate and still be in (or on) the water flow. Once it disappears behind your mounting pod, you won't gain much.

[r&s20]

thanks tuned
the cables actually came off a different boat had to change my pontoon came originally with a mercury motor,they have plenty of slack so i don't believe that's a problem. cavitation plate is hard to see at WOT.

[tuned]

thanks tuned
the cables actually came off a different boat had to change my pontoon came originally with a mercury motor,they have plenty of slack so i don't believe that's a problem. cavitation plate is hard to see at WOT.

That is a good thing to check as well, where the plate 'rides' when running. Yep, hard to see sometimes. Try climbing in another boat or having yours fly by a dock and take a couple pics so all the ummm 'experts' here can have a look.

Actually I was referring to how the plate sits in relation to the bottom of your mount pod, which you can check on the trailer. If that plate is starting to disappear behind the pod, you won't make much further gains by raising it. Most boats have no problem with this, but it is good to check before investing time and money. Good luck.

[Bamby]

Are you utilizing the trim properly? I'm always amazed how many pontoon boats I've observed running along at full throttle ahead with the motor in the full down position. For the best overall performance and ride one needs to utilize their trim to the best advantage. Even on my big heavy boat adjusting the trim is critical for it to do it's very best. When I'm running at speed and I've got the trim right the motor itself generates a lot of lift, and the nosecones themselves are almost clear of the water and it makes for a good ride that catches attention out on the water.

I guess what I'm trying to say is this. Your setup may be close enough to right that when utilizing proper trim angles while underway you may actually find yourself in the sweet spot you're now seeking to create.

[r&s20]

tuned,
i will try posting some pic's. can't get to lake to run boat.lake is over 1 hour away from house and even further for someone else to take pic's or video.

[r&s20]

sorry i screwed up meant to post more than 1 pic.

bamby, thanks for asking but yes i have used trim,i actually find little difference in rpm or speed although to low and sprinkles water on passengers,motor run best at almost neutral can trim full up and alittle more before prop ventilates (using g.p.s. not seat of pants) i think the prop i'm using is not a good bow lifting prop.

[cleatus]

Those wave deflectors, (or whatever they're called) on each side of the motor pod...looks like they could really change the flow of water coming out the back, especially since it's has underskinning. I haven't seen those before, are they factory installed by smokercraft?

Seems to me, those fins could really disrupt the water for a good prop bite, cause drag, or effect performance at mid/high speed.
(disclaimer) I know nothing of fluid dynamics, but I do make a great cannonball splash. heh heh.

[r&s20]

cleatus,

those deflectors are original i think i bout boat at least third hand and where there when i got it.the under skinning me and the wife did last summer.man what a difference that made. i would recommend everybody do it.(i learned about that from the good people here) thank you all

[cleatus]

It seems like the angle of those wave deflectors would act like downed trim tabs, raising the rear, forcing the bow down. What was it like when you were running without the "doel fin"?, one could be fighting the other.
You're right, underskinning is a great addition, I did mine last spring too, but I didn't have any help that weekend so I just used a "deadman" and ss zip screws.

[r&s20]

they may be acting as down trim tabs,hadn,thought about that. if so don't no how to correct than or even if i should try.i've seen alot of pontoons with them but never thought about any effects of them.the 14x10 ss prop i have seemed to be a better bow lifting prop.but wrong for this setup.when motor was at lowest setting back 3-4 ft of toons was underwater so bad that water was being forced up through a drain hole in deck that was no longer being used.

[tuned]

Your DoelFin (generic term Whale Tail) will certainly change running characteristics. I've used several brands on regular boats and pontoons as well, with mixed success. They seem to be very individual as to what they will do for any given boat. Shape and size DO matter

The whale tails are usually used on rear heavy small boats to bring the nose down and reduce 'porpoising'. They can sometimes help faster boats reduce cavitation in turns. Pontoons, they can help reduce straight line blowout. They are pretty good in general to improve hole shot. They DO increase drag to an extent, but sometimes it is offset by the other gains. All a guy can do is try them.

Back to your jackplate: The first shot shows that your motor can go up another inch or so before getting lost behind your pod. A jackplate that gives you setback also gives you more headroom to lift your motor, because the water coming off your pod now has six inches to 'rise' before contacting your cavitation plate. It's not too much, maybe an inch. This would give you about two inches you could go up with a plate, which is all drag reduction. Up to you whether you want to risk the time and ching. I'm not convinced you'll get a whole lot more, but I've proven myself good and wrong in the past. All you can do is experiment if you're feeling frisky.

[r&s20]

thanks tuned,
i believe i'm gonna try a jack plate as you said before i can always resell if it don't help.but will be a while.you how money goes.after i do i will post back with results.