Shorter drives?
#11
Re: Shorter drives?
Originally Posted by jpclear
The new prop design technology promotes running surfaced (higher) with actually LESS slip and more overall efficiency. JULIE... WHERE ARE YOU?? You can explain it much better. --- Jer
It will all come down to trial and error which only amounts to more money...
#12
Registered
Re: Shorter drives?
On my boat when I added the shortie the RPM increased 200 RPM and the slip stayed the same. This netted about 3 MPH compared to the standard length drive. I then re-propped and gained another 2 MPH at close to my original RPM with the standard length drive. I would expect to see an RPM increase unless you completely lose your bow lift leverage and the boat is plowing, then you may lose RPM!
Craig
Craig
#13
Charter Member #927
Charter Member
Thread Starter
Re: Shorter drives?
Thanks Craig. and everyone else too.
I'm running a non stepped V with a transome notch and staggered engines. My prop shafts now when level are about 3" below the V part of the hull (not the notched out part) that is directly in front of them.
That seems pretty deep to me, is it?
I'm running a non stepped V with a transome notch and staggered engines. My prop shafts now when level are about 3" below the V part of the hull (not the notched out part) that is directly in front of them.
That seems pretty deep to me, is it?
#14
Re: Shorter drives?
Originally Posted by WETTE VETTE
On my boat when I added the shortie the RPM increased 200 RPM and the slip stayed the same. This netted about 3 MPH compared to the standard length drive. I then re-propped and gained another 2 MPH at close to my original RPM with the standard length drive. I would expect to see an RPM increase unless you completely lose your bow lift leverage and the boat is plowing, then you may lose RPM!
Craig
Craig
#15
Registered
Re: Shorter drives?
Originally Posted by Payton
Thanks Craig. and everyone else too.
I'm running a non stepped V with a transome notch and staggered engines. My prop shafts now when level are about 3" below the V part of the hull (not the notched out part) that is directly in front of them.
That seems pretty deep to me, is it?
I'm running a non stepped V with a transome notch and staggered engines. My prop shafts now when level are about 3" below the V part of the hull (not the notched out part) that is directly in front of them.
That seems pretty deep to me, is it?
Last edited by PatriYacht; 01-22-2006 at 05:33 PM.
#16
Platinum Member
Platinum Member
Re: Shorter drives?
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
#17
Registered
Re: Shorter drives?
Yes my boat is a cat and it gets bow lift with no trim at speed. If you need bow lift it is possible the sorties will not provide enough leverage. Ya never really know until you try! Good luck!
Craig
Craig
#18
Registered
Re: Shorter drives?
Originally Posted by PatriYacht
That doesnt seem too far off Mark. Mine is about 6 inches below and my boat has a notch and boxes. Glad you found a couple of shorties Harper. I found one, so if you know anyone with another -2 Imco tell them about me.
#19
Re: Shorter drives?
Originally Posted by WETTE VETTE
Yes my boat is a cat and it gets bow lift with no trim at speed. If you need bow lift it is possible the sorties will not provide enough leverage. Ya never really know until you try! Good luck!
Craig
Craig
What have you experimented with as far as drives and props?
#20
Registered
Re: Shorter drives?
It really depends on the boat, what X dim is has on it, and so on. I have a 2000 fountain fever that came with a very low X dim from the factory. When I went from standard length sportmaster drives to -2 shorties I picked up 5 mph and the water pressure went thru the roof. I was turning bravo one 30's around 5100 rmp and after putting on the shorties I was turning 32 bravo ones at 5300. The imco's have a larger water opening so I am going to have to install relief valves to get the water pressue back within limits.