Aright guys I need a little help here. I'm in the process of building a hyperdrive and I'm getting close to the finish but I've got a question. I need to figure out how long I need to make the box that houses the belt drive. So when my boat is on plane how deep should the prop be in the water? Is it half submerged when running flat out for top speed?

Can anybody tell me how far the center of the drive tube is from the bottom of your boat when it's parallel with the bottom of the boat?

Or even easier... What is the distance from the bottom of the belt housing to the bottom of the transom? 3-4 inches?

Here's a picture of the belt housing and drive tube. I know the drive tube looks long and thats because I haven't decided how long I want it yet.

You want enough space between the bottom of the transom and the belt housing so that vegitation, rocks, stumps ect. wont hit it.

The output shaft should be running to the water at a slight angle half the prop in half out while on step. The higher the belt housing the longer the output shaft needs to be but dont get it to high or your motor will run at a too far back an angle and you wont be able to trim down enough when your stuck.

ok thanks. that makes sense. 3 inches enough clearance above the bottom of the transom. I guess i want to make it as long as I can so I can dig in as much as possible in the nasty stuff.

Here is another pic. I've got a honda 16hp clone that I'm gonna power it with. They use this engine for go kart racing so they've got a ton of aftermarket parts for them, and since it's a one cylinder engine, it costs about half as much to mod as a v-twin. The highly modified engines are getting 40-45 hp. I'm gonna add a high lift cam, mikuni carb, and upgrade the valve train and see where that will get me. The coolest thing about it is that it's only going to weigh about 120 pounds. Should work great on a small boat.

well it may not look it in that pic but that prop is 9 x 8. You think thats too small? Im thinkin I will try to get about 30 hp out of the engine. I don't want to make it blow up

Most 30 hp sd's are runnin 11-12 inch props

what is your gear reduction ratio?

How will your trim work?

Top pulley is 34 tooth bottom is 48 so 1.4:1 When I put the motor on it should be pretty balanced but still a little heavy on the prop side so trim is going to me manual but I'm going to use one of those weld on spring loaded pins to lock it in for running across the lake and trailering.

Where did you get all your bearings, seals, drive shaft from?

Got the bearings and seals from mcmaster carr. Got the shaft from some online metal store and payed to have it machined to my specs.

From the looks of that outboard skeg/ prop you are way past due for a mudmotor.

Looks great definitely post some pics and bids of speed when completed.
Quick question what type of stainless steel did you use for the drive shaft?


Your definatley going to need a bigger prop eventually when you make more hp so make sure it is surface piercing not sub surface. I thi k the 9x8 you bought is sub surface. Not sure though but that's what I'm thinking

I turn a 9x7 longtail prop with a slightly modded 6.5 on a homemade surface drive. Look on Ebay for props. I built a 16 already , i think you can turn the 11x10 with the right gear ratio. I run a comet cvt on the 6.5 hp.

With a 1.47:1 gear ratio on a 24 honda I run a 12x12 Godevil surface prop. SO with that much hp and the 1.4:1 ratio, maybe the 11x10, 12x10, 12x11, or 12x12 prop. Only thing is they are mostly hex shaft, Hillmarine will bore it 3/4 threaded, he quoted me $50 for 3/4 bore. It is all trial and error, hope my input helps any.

Woodiebusters your right. I'm way overdue for a mm. I've been wanting one of these things since I started duck hunting about 6-7 years ago. That boat in the pic just won't go where I need to go.

I'm pretty certain it is a surface piercing prop. I used 304 stainless for the shaft. Ill definitely let you know how it turns out.

I sized the prop from looking at the mudbuddy website and comparing it to what they use on each engine. I just looked at it again and I think I confused what I needed with what I would need for a 30 horse long tail. Looks like the 29 hp van runs a 11x10 prop and I believe that motor is geared 1.38:1. I'm geared just a hair lower so I would surely be able to spin it. I guess I'll see if the guys at boat city prop shop up in okc will let me trade this back to them for a larger one. Not counting on it though.

Thanks for the help guys. Wish I would have known about this forum before. I've been stumbling around the internet trying to figure out how to do this right for quite a while.