Custom Hydroplane Gearset?

[johnsonm50]

Looks to be running deep, set up is as key to speed as the right stuff. You are also heavy & worse yet, top heavy with a full fishing motor. There is potential for a good amount more than 50 just that it will be harder to find as you improve & more of a handful to drive.

I was working outside & checking in before, this kind of thing has interested me for a long time. I tried alot of stuff to get an OMC twin 25/35 to go on hydro's n runabouts. 52 was about it till I adapted race gear cases. Your motor on the other hand is much more capable than those old cross flow 2 strokes.. but, more tonnage too. I'm thinking you could probably spin more pitch but keep in mind when you over pitch you lose speed & take off. Finding a way to cool the motor & running a surface prop [a regular prop will most likely not work on the surface] is going to be what does it. Then its a matter of getting it all in order..depth, angle, prop choice, weight & its distribution, airing out the hydro & getting used to it safely. Low to mid 60's should be possible, more would take serious note keeping & test running, speed & rpm data as well as the right stuff. Good Luck, keep us posted.

[ZUL8TR]

Speed projections for pitch

Based on a I-Net search the GR for the Yame 30 is 1.85:1 or 2.08:1 I guess depending on model and year.

For a 60 mph speed here is an estimate of the pitch needed at 7000 rpm assuming your engine can wip prop that rrm and still provide enough thrust to overcome all drag:

GR = 1.85:1 - pitch about 17" at zero slip, about 18" at 6% slip
GR = 2.08:1 - pitch about 19" at zero slip, about 20" at 6% slip

The zero slip is theoretical and is not possible some slip needed. I estimated 6% slip but it could be greater. Only way to know is to run and record speed with GPS and rpm and knowing pitch calculate slip. Speed and handeling has alot to do with: prop design. pitch, prop center height relative to bottom, motor angle, set back, total weight, weight distribution, aero drag, boat bottom and engine lower unit drag, hull bottom air compression lift, bottom hydrodynamic lift, etc.

Calculator used:

http://continuouswave.com/cgi-bin/propcalc.pl

If you go with a Quicki style gear case with forward only all pitche change due to numerically lower gear ratios. Speed and handeling issues noted still apply.

[Dave M]

Tip On Props

Trust a prop builder to provide you with what his or her instincts tell them. Don't try to convince them otherwise. Listen to them. No amount of math or theory can replace experience and or instinct. If Ron is willing to work with you, by all means try 4 or 5 props. It will take that to get the perfect combination.

For height, I am not certain what the stock gearbox has for lift in it, but I would use caution raising it to level with the bottom of the boat. If the gearcase has lift it could casue the rear to break loose at speed. Just be ready for it. That prop calculator is a good first step to be near the ballpark, so maybe start with one it indicates, and then talk to the prop builder about how it reacts on the boat. You can get props that push the bow down, or ones that lift the rear of the boat up, etc, etc. Certain cut of props do specific things.

[hi0npsi]

Is there someone making a new gear case for these motors or someone that makes custom gear cases? Could a machine shop feasibly take the gear set I have and make something with a lower ratio or is there some physical limitation that would prevent that from working/being installed?

Thanks Ron, johnsonm50, ZUL8TR and Dave M for your sage advice. With it in mind I plan to start with either moving the motor up (probably) or had considered having the shaft sectioned, driveshaft cut/spline machined and shift shaft shortened. Adding a low water pickup would obviously be needed either way. I'd like to try one thing at a time so as not to confuse the issue with multiple variables. While I think shortening the shaft is doable, cleaner and lighter, I'd prefer to find out if it still handles OK lifting it first so that if I decide I want to sell this later the motor can be sold separate of the boat.

[T Chance]

I suggest an adapter plate and driveshaft coupler and bolt on a Rossi, VRP or Konny racing gearcase. They come all available with a big selection of gear ratios, 15mm propshaft with shear pin (not splined) and you will have an almost endless supply of 2, 3, 4 and 5 blade real racing propellers. You will lose your gearshift but if you want to go fast this is how we do it in the Pro Division (Mod Division too).

[A/B Speedliner]

Curse at 90?

Ron just having a little fun with you, I curse at 90 all the time but I cruise at 70.
David

[hi0npsi]

I suggest an adapter plate and driveshaft coupler and bolt on a Rossi, VRP or Konny racing gearcase. They come all available with a big selection of gear ratios, 15mm propshaft with shear pin (not splined) and you will have an almost endless supply of 2, 3, 4 and 5 blade real racing propellers. You will lose your gearshift but if you want to go fast this is how we do it in the Pro Division (Mod Division too).

Thank you. If the other adjustments don't make for enough speed I will either go this route or buy a proper racing rig like I probably should have in the first place