Jon boat O/B height

[CruisinGA]

I generally agree... but my buddies single cylinder 6 hp 4 stroke turned lower rpms and was quieter than my old 6 hp... really quiet under 1/2 throttle. I think thru-hub exhaust plays a role here.

[TRBenj]

Originally Posted by CruisinGA

I generally agree... but my buddies single cylinder 6 hp 4 stroke turned lower rpms and was quieter than my old 6 hp... really quiet under 1/2 throttle. I think thru-hub exhaust plays a role here.

Thats consistent with my experience. The later 2-strokes from the 70's and 80's rev quite a bit higher than the 2-strokes from the 50's and 60's (5000 vs. 6500 rpm WOT). Neither is particularly quiet or efficient.

The new 4-strokes are way quieter than any of them, and way more efficient. Theyre also significantly heavier, which is particularly noticeable on these light weight, low hp applications- giving them a significant performance disadvantage.

[boater8987]

You can tell its winter time. Talking about jon boats. LOL I have been looking around for one of those 18 Hp 1950's Evinrudes. My neighbor with his 90's 15 Evinrude says his is fast. We have BS ed about having a jon boat radar run shootout. Like they have a LOTO for performace boats.

TRBenj : Do you have a pic you can share of the jack plate mounted motor & boat?

[TRBenj]

No need for a radar gun... a handheld gps that captures max speed (like a garmin etrex) works great. We use it on the aluminum boats and ski boats alike. The 15hp's we have of various vintage all run 24mph consistently, and have touched 25-26mph briefly under ideal conditions. With a light load, they really haul- enough for my 150lb buddy to ski behind!

I checked and dont have any good pictures of my mini jacker installed... here is the best that I have. I mounted mine as high as I could on the transom, but could not go quite as high as I needed due to the lip of the aluminum at the top (hence the additional board under my bracket)... but its high enough to get a nice solid surface to clamp against.

[EJ OJPROP]

We used to call those boards "rev sticks" when we were racing stock outboard hydros. Used the sticks to run the engine as high as we could and still pump water at speed. Too high = no water as well as not being able to steer.

[CruisinGA]

Mocked up the motor last night while fabricating some transom reinforcement brackets.

1st pic - cav plate relative to transom with motor sitting all the way down on the transom
2nd pic - cav plate relative to transom with motor sitting raised on transom
3rd pic - shows transom bracket position when above pic was taken. Can the O/B be mounted like this? I don't think so?

[CruisinGA]

Pic 1 & 2 shows where the transom started to come apart from the increased stress.

Pic 3 shows the brackets I made to prevent the transom from pushing 'into' the boat and continuing to pull the transom apart. I am also going to run a piece of angle across the bottom of the transom board to stiffen it and help transfer the force to the brackets and sides of the boat.

Unfortunately, I don't have an tig welder with AC (yet) so I tried some of this stuff but my Mapp torch wouldn't get the aluminum hot enough. Just too much surface area to dissipate the heat.

We'll see how well this all works!

[TRBenj]

No, I wouldnt run the motor with a gap under the bracket like that. Build up the transom higher or use a jack plate. Looks like you need to gain another 1/2" anyways.

I would reinforce the transom better if its flexing that bad... a board that covers the majority of the inside (as far down to the floor as possible) is a good start. Those brackets are a good idea too.

[captain planet]

Originally Posted by psychobilly

The horizontal fin on the lower unit should be level with the bottom of the skiff. Oh, and you may want to add a stiffener piece of wood on the transom now before the aluminum starts cracking under the stress of the 9.9. Don't ask me how I know this. 😄

Thanks for that, I got a chuckle out of it.