Surface Drive Gear Ratios?

[Mr. Tom]

Hello All!

I am looking for some info to help me bring a project of mine to completion.

The boat:
23’ Dan Arena Deep V
454 Chevy Full Roller, ~400-450hp
Fixed Arena Surface Drive

Now my question is, I have a Velvet Drive 8degree drop output with a 2.5:1 reduction ratio.

Can I use this transmission with this setup and run a downright huge or aggressive multi blade prop?

I have been told that a 1:1 ratio box is recommended, but some of the reading I have done suggests that reduction gears are better suited to this application.

I was hoping to go with this Trans, as I already have it, and it has the 8 degree drop output, allowing me to mount the engine level in the boat, as opposed to a 1:1 straight thru, where the engine will have to be tilted in the boat, obviously.

Anybody here have any experience with this kind of stuff? Gear ratios for surface drives I mean?



The other question i have is, can i put a Thrust block/bearing in this boat, and just run a Power Glide automatic trans in it?

[baeckmo]

First some further info is necessary in order to evaluate the arrangement:

..Boat weight fully laden,
..Max possible prop dia
..Shaft dimension

[Mr. Tom]

baeckmo,

Prop Shaft: 1-1/4" SS
prop max diamater: ~16"-17"
Boat Weight: ~3,800lbs

[baeckmo]

First rough estimate of shaft rpm for 17" ventilating prop and 400 hp is ~3000 rpm. So, unless your engine rpms are ~7500, you can not use the 2.5:1 ratio. To come closer in ratio, please come up with engine rpm at max power. (sorry, forgot to ask about that before).

Next limitation is torque; your 1 1/4" shaft can not take the twisting of 400 hp at 3000 rpm, so in your case, the shaft diameter > shaft rpm for 400 hp > gear ratio > propeller dia. Frankly, this is a "less than optimum" case of backwards engineering, so the outcome will not be maximum for the power/weight available.

To be precise with the ratio, we need to know the quality of the shaft as there are substantial differences in strength between different ss steels.

[Mr. Tom]

Yes Sir!
This is a mild Big Block, and as such engine RPM will be kept well under 6k, most likely 5,500 RPM at WOT is what I would be shooting for.

I am looking for speed out of this vessel, hopefully over 65-75knts

The boat with the other drive I have shown, similar to mine, runs a small block ~300HP a 1:1 box and attains speeds of about 45knts if I remember correctly. Albeit running a much smaller prop that I imagine I could run.

[baeckmo]

Hah, Tom so you're hanging on there.... now in my corner its just past midnight, so zzzzznorrk until tomorrow!

[Mr. Tom]

No Problem, have a good evening, and thanks for you help!


I do not have the shaft, prop or rudder at this point, however the drive unit is what is determining the shaft size, I believe almost 90% sure it is a 1.25” but may be a 1.5” I will double check that when I get home. I will have to have the shaft custom made, once I figure out the drive/engine combo and placement. Therefor I could get a shaft that is of adequate strength. I am seriously considering using a thrust block, and a short driveshaft if the 2.5:1 will not work, as I also have access to a drag boat powerglide, with a 1:1 final drive ratio.

I was trying to avoid putting the powerglide in the boat, as it will move the engine further away from the transom, and using the thrust block adds complications to the project.

[bertsboat]

He is at Arena Yach sales in San Rafeal. He knows all about these boats. I assume you know Dan arena and Arneson were pals and the first Arneson was in an Arena Craft hull. That boat came with that drive?? Nice project. Glad to see you saving that boat. It should be a great riding hull. Looks great.