Shorter drives?
01-22-2006 | 07:25 PM
#21
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Joined: Feb 2002
Posts: 1,296
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From: LaPorte IN.
Re: Shorter drives?
My boat is a 23' WPM cat with a NA solid roller 598 home built and not dynoed. With a standard length Bravo it ran best with a 30 Bravo at 6100 RPM through 1.36 gears. My x is pretty high and I really didn't think the shorty would help. Luckily I have a buddy that let me try his before I bought mine. With the shorty I turn the 30 6300 RPM and can swing a 32 6000. The slip is essentially the same in all scenarios. Don't you have a 28 Daytona? I have a friend with a 28 and he runs 2" above the sponson on a box. Without a box you will need to be about even with the bottom of the sponson. My propshaft is even to 1" above the sponsons. Obviously mine is a single. Good luck testing!
Craig
Craig
01-22-2006 | 07:58 PM
#22
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Joined: Jun 2003
Posts: 1,496
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From: Omaha~LOTO
Re: Shorter drives?
Originally Posted by WETTE VETTE
My boat is a 23' WPM cat with a NA solid roller 598 home built and not dynoed. With a standard length Bravo it ran best with a 30 Bravo at 6100 RPM through 1.36 gears. My x is pretty high and I really didn't think the shorty would help. Luckily I have a buddy that let me try his before I bought mine. With the shorty I turn the 30 6300 RPM and can swing a 32 6000. The slip is essentially the same in all scenarios. Don't you have a 28 Daytona? I have a friend with a 28 and he runs 2" above the sponson on a box. Without a box you will need to be about even with the bottom of the sponson. My propshaft is even to 1" above the sponsons. Obviously mine is a single. Good luck testing!
Craig
Craig
01-23-2006 | 08:50 AM
#24
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Joined: Jan 2001
Posts: 4,834
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From: IN
Re: Shorter drives?
Originally Posted by BenPerfected
Payton,
I run a non-stepped V with twins and my prop shafts (when parallel) with the bottom are .75" below the bottom. I get on plane a little slow with Bravo 1's in a 30' hull @ 8,000 lbs. (dry).
I started at 4.25" below (including a 3" spacer) w/27P Mirage props at Lake X. Base line was 97 MPH w/ Imco 2" shorties. Switched to Bravo 1's (same effective pitch; 27p Mirage to 28p Bravo 1). At this point we started reducing the spacers...2", to 1" and then to no spacer. The only significant change was the speed increased each time we raised the drives 1". We ended at 103MPH+. After a re-rig, the following year I tested at .75" below the bottom vs. the final 1.25" from the previous year. No change in speed. In my straight V, 1" below is close to optimum.
Sprague
I run a non-stepped V with twins and my prop shafts (when parallel) with the bottom are .75" below the bottom. I get on plane a little slow with Bravo 1's in a 30' hull @ 8,000 lbs. (dry).
I started at 4.25" below (including a 3" spacer) w/27P Mirage props at Lake X. Base line was 97 MPH w/ Imco 2" shorties. Switched to Bravo 1's (same effective pitch; 27p Mirage to 28p Bravo 1). At this point we started reducing the spacers...2", to 1" and then to no spacer. The only significant change was the speed increased each time we raised the drives 1". We ended at 103MPH+. After a re-rig, the following year I tested at .75" below the bottom vs. the final 1.25" from the previous year. No change in speed. In my straight V, 1" below is close to optimum.
Sprague
Well, here I had decided I didn't need to try them. After reading this, maybe I do need to give it a try.
I've got a 32' running surface, 25 degree V and I would guess about an 18" notch. I run labbed, 25" mirage+s. A friend has a set of labbed 26" Hydros I could probubly get for about what I could sell my Mirages for.
Maybe I need to start thinking about this again.
Setup on a lower unit is pretty simple, right? Just torque the verticle nut and set preload on the carrier nut? And get everything in the right place.
01-23-2006 | 09:20 AM
#25
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Joined: Sep 2002
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From: Lake St. Clair
Re: Shorter drives?
Every application is going to be different - TESTING - is the only for sure way to know - I know on my application (35 Fountain single step) the RPM increased by 200 - up 2" & up 2" prop pitch netted me 5 MPH
01-23-2006 | 05:08 PM
#27
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Joined: Oct 2000
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From: Western Michigan
Re: Shorter drives?
Originally Posted by BenPerfected
I run a non-stepped V with twins and my prop shafts (when parallel) with the bottom are .75" below the bottom. I get on plane a little slow with Bravo 1's in a 30' hull @ 8,000 lbs. (dry). We ended at 103MPH+. Sprague
1) Does your boat have a notch in the transom?
2) Did you notice any increase in speed at your cruising range....let's say 3500-4000rpm?
Thanks
01-24-2006 | 05:04 AM
#28
Charter Member #601
Joined: Dec 2000
Posts: 3,276
Likes: 5
From: Holland, Mi USA.
Re: Shorter drives?
Payton,
Gear lash has to be set up.. Pinion height and driven gear depth.. The Imco lowers are different than Merc cases. Well the number of shims are different to get the same pinion ht..
Dick
Gear lash has to be set up.. Pinion height and driven gear depth.. The Imco lowers are different than Merc cases. Well the number of shims are different to get the same pinion ht..
Dick
