Prop wash over transom

[A.F.C. 8511]

Took boat out for first trail run and some engine break in time. Getting some prop wash over transom and turbulant water at rear on both sides of transom at high speeds. Its an older "U" shaped pontoon log boat so it runs shallow.
think if I "skinned" the underside rear 1/3 it would help smooth that heavy turbulence in water at transom and stern?

 

[GA_Boater]

How low is the motor on the transom?

Raising the motor some may help. Got pics of the motor showing the setup?

 

[HotTommy]

I'm not sure what "prop wash" means in this context. This video shows the underside of a pontoon boat with water pushed up and out by the logs hitting the bottom of the boat near the center (where the engine pod is). It demonstrates why skinning the underside can reduce drag and increase performance some. It would also explain turbulent water on each side of the engine pod. But I wouldn't expect this to cause water to come up over the back of the transom. .... As was mentioned above, some photos would be helpful in understanding your situation.

 

[ahicks]

Not sure how "prop wash" could be getting in front of the engine either. It does leave me wondering, like GA_Boater is, if the engine has been mounted way too low. If that's the case, often you will see water riding up the front side of the engine, creating all sorts of splashing in the transom area.

 

[Scott Danforth]

How low are you sitt8ng? Are the logs waterlogged?

 

[A.F.C. 8511]

When I get it back in water I will get a video and pictures.
the logs are solid. No leaks, not saturated or taking water.
boat is 1983 JFG with "U" shaped logs. It runs low in water anyway. But not bad. I really think its the turbulant water and the fact I mounted transom back 16 inches. But the motor has this intelligent trim thing. So it AUTOMATICALLY trims down looking for clean water. (motor is 2018 Mercury CT Pro XS 115. Alot of new motor on alot of old boat...lolol.
I gotta marry the two up

 

[5150abf]

Nature of the beast, you have two hulls side by side so the wake from the tubes has nowhere to go.

The underside of a toon at speed is a mess for sure, if you can solve this problem you will have a much nicer house as every pontoon maker will buy it.

As stated, skinning the underside will help cure surging and give you a bit more speed but the turbulence is here to stay.

 

[silveraire]

Agree with 5150. I have underskin on my 24' and it helps, but once you reach anything over 20 mph it starts to get wet. When you hit 30mph everything gets drenched. We tried all sort of motor heights and props to no avail. Nature of having a 2 log toon. That's with a 16' mercury 115CT and 23" logs.

 

[icwingman]

its always going to be there when going fast, i was even thinking of making a deflector to mount back there

 

[Cat nip]

I made some small deflectors for the frankentoon and hope to try them out today. I will let you know how and if they work

 

[Cat nip]

Ok i have had a chance to try out the deflectors i cobbked up and they do work to keep the spray off the motor. Now to be honest the first time i took them for a spin was after i removed my kicker and bracket and the water was glass and i had no spray of any kind at 19 mph and the plywood underneath was dry as a bone. But the second time the water was a little choppy and i could tell they were working because i was feeling the surging from water hitting the crossmembers but the only water i saw from the back was barely enough to get my steering cable wet at 19.5 mph and thats all shes got captin. I made them from 1/8 aluminum sheet salvaged from the fins off my old transom. So they were already ore bent to about 45° and they are about 2" in either side of the bend and 15" long each to fit between the tube brackets and the transom.

 

[Sea Rider]

Post a video on what's going on at back of engine. If water flow at speed is passing right over the upper small plate area water splashes will be produced there, water needs to skim right under the small upper plate right where the cutting edge is located. Need to raise engine accordingly to match that particular height spot to fully cancell any unwanted water splashes.

But if lower leg at speed is receiving highly disturbed middle water wake produced in between tubes while flowing aft along a non ideal engine-transom height match it's a complete different story.


Happy Boating