Vibration Affecting Prop Slip

[JohnsonM50]

It does look cool but I'd guess 60 a tall order as deep as the prop is running. 50 is a big hurdle for non aired out designs w/non surface riding props but wouldn't be surprised it its there & no doubt has acceleration.

[pdt]

I do like that red top cover, and it don't look wrong on the older bottom half.
I see the boat was just cut off and shortend at the back, this explains why the transom looks so wide.
looks a bit longer than 9ft though !!! but this must be a quick little rig.
I would think the bigger block is causing the back end to dig in too much, and this can also cause vibration !!! ive had that before when over powering small boats.

ive seen other pics of this top cover and im amazed just how good it looks, is it fibreglass and did you mould it yourself ?

would be nice to get it all smoothed out, as it does look a very cool engine, and the bottom looks in great condition.
I would say its a weight on the transom issue causing the speed/ vibration problem.

have you tried it by putting say 20 pounds in the bow to counter the extra transom weight / if it stops a bit of vibration you would atleast know your problem.

I had a very tiny boat years ago with a 6hp on the back, I took that off and put on a very good 15hp and had similar problems, I then put ballast up front and the boat was a lot quicker
and it did not vibrate anymore.
just a thought.

[omcstratos]

It's a 9 footer. Since it's used as a dingy, hanging off my cruiser, the construction is extra rugged (read, heavy). THe "smaller" motor, te external reeds triple, can be seen in the background (with the candy red hood).

Jeff

What's the copper thing at the cav plate for??

[pdt]

I bet that's what he uses for running it up without a water butt
sort of water inlet to the prop place that water normally gets pushed up to.

just a guess

[OUTBOARDER]

30 lbs over weight cant air out

[Fastjeff57]

Thanks for all the nice comments!

The hood is a fiberglass one off. I've worked with that stuff for decades. (See photo of the kit cars I developed.)

That copper line goes from the water pickup to the pump inlet. I located the pick up on the left side, so the RH prop flings the water into it. Must work, for that big PH stays dead cool with the small Mark 55 type impeller.

On running attitude...For some reason I can't get the bow of this boat to run up. It'll porpoise a bit with all the motor trim out it will take without cavitation at part throttle, but the bow drops and stays down whern I mash it all the way.


Still learning after 50 years of running little boats!

Jeff

[pdt]

the boat will be bad for running attitude, the running suface has been taken away when shortened.

lots of people have shortened boats by enough to lose the running suface, when looking at the side on pic this looks like that is whats been done.
was this boat about 15ft before it was cut ? or maybe even a 17 footer ?
you have the deep v part but not the rest of it.

I had a model boat and done very similar thing to it, it was brilliant at 5ft long yet at 3ft was waste of time and just would not run right.
probably find a setback might put it right, not jacked up set back just a foot or so to see what happens.

does this also kick up a lot of spray at the transom ?

[MWhite]

It's a 9 footer. Since it's used as a dingy, hanging off my cruiser, the construction is extra rugged (read, heavy). THe "smaller" motor, te external reeds triple, can be seen in the background (with the candy red hood).

Jeff

Jeff I know where there is several of these motors, like the ones in the picture that are for sale they have white cowlings with mercury on them,, just guessing from the 50 and 60s model complete motors, blocks, cranks u name it,,, the owner past away and his wife is wonting to sale all of it. Hes got some ss25 merc with stacks on them ready to run, theres a lot more, any one interested in this kind of stuff let me know.

[Fastjeff57]

The boat was designed (by Bob Dillon) as an 11 foot 11 incher. I shortened the BOW end by making it very blunt so it ended up 9 12/2 foot long. The AFT end is as he designed it.

I'm up to my ears in old Mercs, but the guys at Johns Old Merc site would love to kow about those Mercs

Jeff

[JohnsonM50]

1 Q remains, how fast has it gone so far?