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prop selection

Old 08-23-2004, 12:10 PM
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Question prop selection

I have a 1982 38ft Cigarette with normally aspirated 600HP and TRS drives. Before I refurbished the boat I
had 26p 3 bladed cleavers. At that point the boat had about 500hp per side and the boat would run about
69mph on the GPS @ 5400 rpm. I since then have put a set of 4 blade 26P Hydomotives and the boat has a little better cruising speed but I only can run about
59 mph at 4900 rpm. I am more interested in cruising
but is there a prop in between these I should consider.
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Old 08-23-2004, 12:44 PM
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Default Re: prop selection

Don't understand why you would loose 10mph with the Hydro's after adding 100hp per side to the boat. Three blades are almost always faster than four, but never that bad.

Did you add extra weight during the refurb? Did you paint or modify the bottom of the hull? Make sure there is no water trapped in the front of the hull, as in front of the fuel tank, from a clogged drain? Did you change the rotation of the drives? Are you sure you really added 200hp more than your old engines?

69mph on GPS is quite impressive with twin 500hp in an older 38. Try the three blades again to duplicate those figures and rule out bottom problems, like a hook or power hook from a weak bottom/rotten stringers.

Good luck
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Old 08-23-2004, 01:12 PM
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Default Re: prop selection

mike, i agree... something doesnt sound right.. i'm running TRS drives and 26" Bravo I props on my cafe racer...and i estimated my HP is around 600 per side. I am also able to run 4900 RPMs at WOT. I dunno hw fast i'm running, but probably somewhere around 69mph

what does all of this mean? sounds like you need to go down in pitch to get the revs, but that doesnt make sense...unless your baseline numbers are inaccurate...
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Old 08-23-2004, 02:48 PM
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Default Re: prop selection

It does not make any sense to me either. Same rotation
on the drives and the boat is mostly stored inside and I did already make sure the drains were cleared. I did put
in a small a/c unit and 15 gallon water tank.

The original set up was from Hawk. Started with a 427 tall deck stroked to 496 with Chevrolet HP heads. I do not know the cam specs. Tom at Chief engines told me these
engines put out around 480HP. I have rebuilt the motors
using a larger hydraulic roller Crane cam (HR-306-2s-14-ig). Merlin heads (310cc) Team G intake and new Stainless
marine exhaust and Thunderbolt ignition I used to have 1050 dominators but switched to 850 Demons. Based on
this information I had these figures ran on a desktop
dyno and at 5000 RPM the motor is putting out about
580HP. At 5500 RPM it is 620HP. If it is accurate I do
not know.

I just sent my clever props off to get them refurbished. I will let you know how it runs when I get them back.

Thanks!
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Old 08-23-2004, 03:24 PM
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Default Re: prop selection

Sean .. sounds like you need to run a set of 24"s ... get up around 5200 and I'l bet you'll run close to 75

G
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Old 08-23-2004, 03:26 PM
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Default Re: prop selection

Originally Posted by 38cigmike
I have a 1982 38ft Cigarette with normally aspirated 600HP and TRS drives. Before I refurbished the boat I
had 26p 3 bladed cleavers. At that point the boat had about 500hp per side and the boat would run about
69mph on the GPS @ 5400 rpm. I since then have put a set of 4 blade 26P Hydomotives and the boat has a little better cruising speed but I only can run about
59 mph at 4900 rpm. I am more interested in cruising
but is there a prop in between these I should consider.
I don't think those Hydromotives are carrying the bow enough ... you're running too wet ... try a set of Bravos

G
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Old 08-23-2004, 05:03 PM
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Default Re: prop selection

g, thanks for the advice...i rarely run wot and propped the boat for a 50mph cruise at 3400...so im pretty happy with the props...

i will borrow a set of 24s to see what she'll do though

mike...for a reference, I'm running 540 tall decks with team g manifolds and 1050 dominators. some say that's too much carb, but i've got them jetted just about right and i've also heard that the demons can be a real bear to keep properly adjusted.

as for the desktop dyno, i'm curious about my hp and i'm basing my estimate on the engine builder has told me...what information can you use to determine hp? Ive heard of the desktop dyno...can you tell me more?

as far as your boat goes, you've added at least 100lbs which is contributing to the slower numbers, but to be honest, i think you are wasting your money on getting those cleavers labbed...i've got two sets of over the hub cleavers...24" and 25" from mine and i was told they would make good paperweights...the new technology is more blades...not less
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Old 08-23-2004, 06:33 PM
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Default Re: prop selection

Mike, I have an 85 38 FlatDeck Fiberglass (not Kevlar) with 550 h.p. per side running TRS's I don't know how you checked your original speed but that does seem high. I run 24 Hydromotive 4 blades and turn them right at 5000 on a good day and with a 1/2 tank of fuel 130 gals on the GPS I got just about 66MPH.
I tried 26 Bravo ones and picked up about 200rpm ands about 1MPH.

With 25 Mirages (not plus) I got 5200 and 65mph.

Mark
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Old 08-24-2004, 09:11 AM
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Default Re: prop selection

You can find the software I was talking about at
www.motionsoftware.com. I always check my speed
by GPS.
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Old 08-24-2004, 09:57 AM
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Default Re: prop selection

Originally Posted by 38cigmike
You can find the software I was talking about at
www.motionsoftware.com. I always check my speed
by GPS.
I have had more than 15 TG with 550HP-600 HP all running 4 Blade Hydros, they like the transom lift. Each ran between 73 to 77 MPH is your GPS set to Statue Miles or Nautical miles? Also was the motor dynoed with all the marine hardware? each of the hardware such as seapump requires HP to turn and dyno runs without this show false numbers.
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