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  Sal.....quickie on props.

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Author Topic:   Sal.....quickie on props.
Bigshot posted 10-03-2003 11:43 AM ET (US)   Profile for Bigshot   Send Email to Bigshot  
I have a 20' Hydra-sports with a 225 Johnson ocean runner(all 1994). The hull is Kevlar but still weighs a hefty 2300lbs. Engine is another 455, gas is 85 gal cap and it also has an alum. T-Top(200 lbs?). I just removed the engine to install a new steering system and trim motor so I raised her up another hole. She is now on the 3rd hole from top and plate is close to 2" above hull bottom. I can get close to 6k(redline) with 1/4 tank and 2 guys spinning a 14.5x19 OMC SST prop. Question is I also have a 13.75x21 Michigan SST, do you think the smaller diameter may make a difference or is she too heavy for a small diameter/bigger pitch wheel? I know I have to try it but it needs a recon and before I waste $70 am I wasting my time and money by trying? I also ordered the steering cables 1' longer so I can do a jackplate in the spring, maybe the 21 will work then if not now.
lhg posted 10-03-2003 01:38 PM ET (US)     Profile for lhg    
If I can butt in here, Nick, on prop design? I would recommend either an OMC Raker, or Merc Mirage Plus prop ($415) for your rig. You need something that will give you lift, venting and surfacing operation, and the standard SS elephant ear props won't do that. The Stiletto or Rapture props would be a lower cost alternative. I would guess that the boat will run in the mid 40's, maybe as much as 48 depending on tee top drag.
Bigshot posted 10-03-2003 02:15 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
On a good day she gets 50. Hydra-Sports claims 53-55 without a t-top and 50-53 with. I call BS on that but I know she will do 48+ on any day. My bud has a 96 or 97 outrage 17 with a 150 and I take him by a few mph so I have to be pushing 50.

I thought about the raker and just passed one up in the 19" pitch mainly because it was a 14.75x19, I don't want more diameter. I am not unhappy with the 19 but just farting around and once I jack her up, I know I am gonna need something better or maybe even a 4 blade if I go hydraulic lift.

Tom2697 posted 10-03-2003 03:09 PM ET (US)     Profile for Tom2697  Send Email to Tom2697     
I read somewhere that every 1/4" diameter change is about 100 rpm. Most agree that 1" pitch = 200rpm. So, it looks like you should drop RPMs by about 100 rpm. I would give it a try it if it's in decent enough shape. What do yo have to lose except 20 minutes of time and a cotter pin?
lhg posted 10-03-2003 04:56 PM ET (US)     Profile for lhg    
Nick - don't worry about diameter and leave that to the prop designers. The extra diameter on the Raker, and Merc Mirage, is for elevated running and lift. Props are to bought by design and application, not diameter.

Kingfish has a 225 OMC on his 22 Whaler, and the Raker prop seems to run very well, at about the same speeds you are talking about. Don't know what pitch he is running. I'd get a Raker or Mirage if it were me. Spring for it!

Sal DiMercurio posted 10-04-2003 12:27 AM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
Bigshot, if it's a Michigan Raptor s/s it's very, very close to a Stiletto.
Your only looking at 1/4" off each blade to get down to a 13.75 so it's no big deal.
I think you should drop about 300 rpms by going to the 13.75 x 21 plus the Michigan should be more efficient then the mouse ear omc.
That would bring you down to 5,700 rpms but should increase your speed my a few mph, it will also change the way your boat rides by lifting it more, providing it's a Raptor.
The Raptor will tolorate more height if you choose to raise her again to the last holes & will not break loose like the stock sst.
By raising the engine another hole you should gain back another 100/150 rpms to put you right back around 5,800/ 5,900 rpms.
Hell, try it, you may really like it.
Let us know the results.
Hey, what the hell did your Marlins do to my Giants today .........4/3 in 11, their hot.
Sal
outragesteve posted 10-04-2003 03:37 AM ET (US)     Profile for outragesteve  Send Email to outragesteve     
I agree w/lgh: let the experts (Merc) design the props, choose your application, and prop your boat by pitch v.s. rpm (max) and then decide. Just because one boat does "x" mph and another same does "y" mph may not be just the pitch/diameter: if you parked any two production boats side by side, and tried to "blueprint" the bottoms, you would see a measurable difference in the same two hulls from the same builder on any given day...

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