Question For ALLAN BROWN

[J&K SHAHBAS]

Hope I can pick your brain, Im in the middle of restoring my 67 sportsman 28 Im releaving the 327s of there duty and installing 600 ci fords.
im keeping the v-drives. my question is did donzi change the propshaft centerline when using big block power or did the driveshaft enter the v-drive at a angle? also curious about how much % of gears you used in the early race boats mine has 21% underdrive with the smallblocks. My motors will produce roughly 800hp each where do you think for this boat would be a good start in the gears. Thanks for your time and knowledge. John Shabas

[ALLAN BROWN]

If you still have the Crusader 4000 Vee Drives, you are in deep doo-doo. They are rated for 4000 INCH-pounds of torque. Gorilla motors like yours will break the clinch bolts and shoot them out through the side of the boat(not guessing). Shaft centers are OK for any application. We had the strut depressions built into the mold. Find out what you have for Vee Drives and let me know. Since you have limited "drop" in the struts, you are stuck with about 16" diameter. I would be glad to recommend everything that you need. Lemme hear.

[J&K SHAHBAS]

Thanks for the reply,your right the boat does have crusaders, my friend out west at bergeron engineering will build me some casales for it when I give him the gear ratio that I think will work with my engine and style. This has to be the heaviest 28 boat I have driven but only hits about 30 mph with the 327s its got to be fun at 70. Thanks for all your help.Looking forward to meeting you in person.

[ALLAN BROWN]

If 70 is a good number for speed, give me the engine rev's, and I will give you the ratio and the prop size.

[J&K SHAHBAS]

Im just guessing and hoping for 70, Im basing this on my V-Dive hornet its got the same motor a 565 871 blown 6psi boost dyno 790 hp at 5200 and runs about 75. Ive had great luck with this combo so this is what I am building for the 28 do you feel that 70 mph is a realist goal for this hull and weight. I had Menkins in AZ. build my prop for the hornet 12x16 ss and have had good all around performance, but would like to find a more local prop shop, are there any in fla. Thanks,john

[ALLAN BROWN]

John Rose, ex US engineer for Rolla Props, owns Ellis Propeller in Jacksonville, Fl. 904-354-8233. He is a smart SOB and a great guy. You should start with 15" diameter. I like 15 degree rake for that boat. With a diameter/pitch ratio of 1:1.3 or 1.5, or about 19" of pitch, you need 4800 app. With 5200 at the engine, you need 1:1.1 or 1.2 reduction. I like a 3 bladed wheel. Let's roll!

[JOHN SCIBERRAS]

John and Kathy, Iam following this discussion with great interest.Very interesting. Allan Brown really knows his stuff. It will be interesting to see how the project turns out and what speeds you attain.Regards,John Sciberras.

[patp]

Mr. Brown, I was hopping that I could also pick your brain? I have been asking almost the same questions that John has just asked you except I have a few less horsepower. I also own a 1967 Donzi 28 and I am trying to figure out what props would give me the best cruising speed. I would like to cruse at 32 mph at 3000. I am not running the original 426 Chryslers 290hp, they have been replaced with twin mercruiser 454's 340hp each.. The maximum recommended rpms 4000 - 4400. I am still using the original transmissions and v-drives with a 1:1.0 ratio. The props that I am currently using are Michigan dyna - jet 14 x 15's Nibral Cupped. The performance I am getting out of these props is 28mph 3000, 32mph at 3200 and 43mph at 4200. Would you recommend a different prop or would you underdrive v-drive and change the prop. From what I have read and what people have told me you probably know more about the donzi 28 than anyone else I have had contact with so your help is greatly appreciated.
Thanks, Pat

PS: do you still drive with a flare pistol in your pocket?

[ALLAN BROWN]

Pat P.,

We have an old saying...."Figures don't lie, but liars figure.... I think that you are mistaken about the ratio in your Vee Drive. Using your numbers, 3000 rpm x 15" pitch divided by 1056 (factor that takes into account 5280 x 12 divided by 60 etc), your no-slip is 42.61 mph. 28 mph divided by 42.61 is .656. There is no way that that combination slips 34.5%. If you can't read the numbers on the Vee drive, mark the flanges and turn them over a few time and see if the marks stay together or migrate apart. What is your top rpm? If 4200 is tops, then you will lose a proportionate amount of rpm for your increase in cruising speed.

Lemme hear...

[patp]

Allan,

I did get the 1:1.0 ratio off the plate on the v-drive. That does not mean that someone that owned the boat before me did not change the gearing. I will get out there this weekend and mark the flanges like you said to determine what the actual ratio is. What would be an acceptable % of slip for the boat? Because at 3200 rpms the boat is moving at 32 mph which reduces the slip to 30% (that still sounds high).

Pat

[J&K SHAHBAS]

Brownie, thanks for all the advice, this boat is going to look like it poped out of the mold by june at that time everything will be ready to assemble and I hope I can continue to get advice on some hardware installation. Then maybe I can talk you into some driver training in the middle of the gulf with madpoodle in hand for some digital air time shots.OH and about the name on the back? How about BROADJUMPER TOO !

[ALLAN BROWN]

That works for me!

[patp]

Allen,

I looked at the v-drives again today and marked the flange and rotated the shafts. The v-drives have a 1:10 to 1 reduction. That makes a big difference in the slip %. What type of prop would you now recommend for the boat (what rake, diameter and pitch will work best)? Sorry if I am asking beginner questions but I know nothing about v-drives or props. Johns boat sounds great, bigger hp is on my Donzi wish list.

Thanks, Pat