prop ventilation or other ?

zippytc

Cadet
Joined
Mar 22, 2017
Messages
8
Hey everyone new here, and not sure if i should post here or the toon section, but hopefully i can get some help. I have been handed down a 26' toon of an extinct make, i guess its a western boat but have had trouble finding any real info on it. Im haveing trouble with what i would call prop ventilation as when im boating through out the rpm range i will get random rpm spikes and it feels like it looses grip/traction. It has a 1983 evinrude 115 2 stroke with a long shaft (20") and i am running a 13.25 x 13 4 blade solas prop. The engine is as far down as i can get it without adding a 5" extension but is, as i see it, still sucking air. I think i need to drop lower in the water atleast an inch but the local boat shop is trying to tell me that my pitch is to aggresive and its taking to much bite which is why it sucks air. I am rebuilding this toon and sadly dont have a working tach so i cant say what rpm at any point from slow to fast but i feel the "ventilation" in mid to high rpm and when turning at low/mid speed. I can definitely feel when the prop bites cause the 115 will really start to push the boat enough that everyone not ready for it has to grab some footing. From anyone that knows better then me, which is most of you im sure, does this sound like a pitch problem or a depth problem?

this is the best video i have of the last time i took it out for a test run, running at about wot i had to trim all the way down which plowed the bow and it gets some serious spray, worse then what is in the video. In my mind trimmed down and still venting i feel like i need to be deeper but could it be as simple as a bad prop choice ?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,306
move something from the bow to the stern (cooler, anchor, etc)
 

Scott06

Vice Admiral
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Apr 20, 2014
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5,543
You may want to check the hub on the prop, assuming it's an older style rubber pressed in hub. Take prop off and mark center splined hub vs the prop it self , put it back on run it then recheck if your marks are still lined up. If the hub slipped they won't be lined up any more. If it is slipping can be easily repaired by a prop shop
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
Messages
12,345
BTW, Welcome to Iboats,

Yep, check if prop is spun, if so, repair prop, that's your starter prop. if not spun , distribute deck weight evenly. If OB sits at the sweet transom height should produce a flat middle wake at rear lower leg. Anyway, sit OB for water flow at speed to pass right under small upper water deflector plate with OB trimmed to 09 deg to achieve the best propulsion.

Without a tach, that OB is lost. Get an induction tach, need to know if OB delivers at least middle to max wot revs as currently loaded. once those numbers are known can go for less prop pitches to pull wot revs up. Post results.

Happy Boating
 

Maclin

Admiral
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May 27, 2007
Messages
6,761
Once a rubber hub has spun it usually won't hold for any rpm above idle, especially with a 115hp pushing a heavy load, but still worth checking the hub even with a Solas, just to eliminate causes. If prop checks out I can see a jackplate in one possible future if you do not have one on there now,
 

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
Is the prop a ventilated model? Sometimes in rough water a ventilated prop (without the plugs in) can act like that. From the video though it did not seem like you were in rough water that time. If it is ventilated and the plugs are out, see if you pop some plugs back in.
 

zippytc

Cadet
Joined
Mar 22, 2017
Messages
8
wow thanks for all the quick replies everyone. When i first took possession of the boat we rebuilt the lower unit and did replace the press in rubber hub (probably should have mentioned that, sorry) but next outing i will make sure and index it just to make sure it is not spinning.

Maclin- the prop is not ventilated its solid with no holes. I personally think that i need a jackplate to lower the outboard a bit but i was told that if i used one to lower that it would affect my tilt and would obstruct the steering gear ect.. ect.. i dont know if that is true, i feel like it is normal to use a jackplate to drop an engine but i am new to owning a toon.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,286
What Scott said is bang on.
Looks to be clearly running very bow heavy. Can you get any more weight aft ?
The engine doesn't look as if it's trimmed right down either....but the main issue is that the bow is ploughing.
Either need an xl shaft or get her squared up.
 

zippytc

Cadet
Joined
Mar 22, 2017
Messages
8
The boat is stripped down with no seats or coolers except a bench seat in the back other then that just the weight from who was on it and we had everyone moving around to see what would help, oddly enough putting everyone as far forward as we could without being outside the railing helped the most and got rid of the splashing completely, which baffled me but hey it happend. and the engine was trimmed all the way down because anything above that and it would ventilate alot which i know being trimmed like that caused the ploughing.

I think i need an xl shaft but the guy at the shop is trying to help me save money and is confident my issue is prop pitch which is why i came to the forum for just another opinion which it seems like everyone who has answered seems to say 1. make sure the prop is not spinning, which im 99% sure it isnt but i will mark it and check just to make sure and 2. i need to drop in the water

flyingscott- the tach was broke and will be fixed before the next test but all cylinders have great compression and the motor is a solid 2 stroke beast, just prop issues.

i hope i can get back out this weekend and test again.
 

ondarvr

Supreme Mariner
Joined
Apr 6, 2005
Messages
11,527
The waves created between the pontoons can do weird things, so moving the weight around doesn't always do what you may expect it to, and can change a great deal with the exact speed.

​Some people will scream, but this is what a fin or foil is designed to do, it will help prevent air from being drawn down in the low pressure zone in front of the prop.

​I'm not saying it will fix it, only that it would be a low cost method that may help a great deal.
 

Sea Rider

Supreme Mariner
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Sep 20, 2008
Messages
12,345
First video does not contribute much clarifying at which lower leg height is water flow passing at speed. Have other boater tfollow toon at back close enough to check that. Deck weight must be even distributed, OB timmed at 90? and toon running on flat calm no wind water cond at wot.

Happy Boating
 

walleyehed

Admiral
Joined
Jun 29, 2003
Messages
6,767
If you happen back to this post, pitch ain't the issue and it isn't the hub. You have something fwd of prop path that is inducing ventilation...such as a dinged leading edge of either the skeg or the prop itself. It's pulling down hard, like maybe 4500rpm hard (Too hard) and when it vents it cuts loose that's why in a turn it's worse. It could also be just a terrible prop.. either design or condition but this is NOT typical of the solas 4-bld design. If the engine was too high, it would vent for a Looongg time and hook up really slowly. That's not what I see in video.
 

Sea Rider

Supreme Mariner
Joined
Sep 20, 2008
Messages
12,345
An OB on a badly height seated transom will not produce prop venting all the time, depending on lower leg height will vent on choppy, wavy or windy water cond and at close tight turns. Will vent some on non calm water cond, will work fine on calm cond at straight water course.

Happy Boating
 
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