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Author Topic:   Top End Speed on 25 Revenge
Tates posted 07-20-2002 09:46 PM ET (US)   Profile for Tates   Send Email to Tates  
Was wondering what top end speeds in calm waters others have for a 25' revenge HT w/twin 200 hp Mercs on a Whaler drive.Mine is 38 knots @ 5400 RPM, however the Prop calculator shows it ought be closer to 48 knots. I have a 21 pitch & 1989 Black Maxs with 3 carbs.Any response will be greatly appreciated.
OutrageMan posted 07-20-2002 09:57 PM ET (US)     Profile for OutrageMan  Send Email to OutrageMan     
Sound abour 2-3 mph slow, but about right.

The prop calculator is designed for selecting props and not calculating an accurate top speed. It uses some pretty broad criteria such as weight and/or length, and does not take into accout wind/water drag, hull type, etc.


jimh posted 07-21-2002 12:17 AM ET (US)     Profile for jimh  Send Email to jimh     
Which propeller calculator are you guys talking about?

If the 200-HP Carbed Mercs have a 1.87:1 gear ratio, when they turn 21-inch props at 5400 RPM and only reach 38-Knts, that implies a slip of 23.8 %. That seems quite high.

Also please confirm the units as nautical miles per hour (knts). If those are statute miles per hour, then those props are really spinning , i.e., slip is 33%

Tates posted 07-21-2002 11:04 AM ET (US)     Profile for Tates  Send Email to Tates     
The prop calculator I refered to is on the opening page of CW.I'am as we write ,having the props checked for balance slip & pitch, I refered to 38 Knots = 43.7 mph, I was wondering what others are getting.I will have the props back next week I will post the results. Thanks for the replies. TT
lhg posted 07-22-2002 06:25 PM ET (US)     Profile for lhg    
Mercury's prop catalog shows 21" props on your engines at a speed range of 49-56MPH.

My guess is that you are overpropped and should be running 19" props. Those should still give you 51MPH, which sounds about right for a Whaler Drive model. A hard top is a speed killer, with it's weight and wind resistance. With similar engines on my 25 Outrage, I run 21" props when heavily loaded, and still get 56mph out of them.

As JimH mentioned, your figures don't calculate properly, with 5400 RPMS and only 44MPH using 21" props and the 1.87:1 gear ratio.

Your engines could also be mounted too low on the Whaler drive. They should be in the 3rd or 4th holes up. I would recommend that you be using Mirage or 4 blade Offshore props.

Tates posted 07-22-2002 10:13 PM ET (US)     Profile for Tates  Send Email to Tates     
Thanks for the input,The engines are mounted in the #3 of 5 holes counting from the bottom.I believe that prop slip may be the culprit, is that corrected by changing props and adjusting engine height?(trial & error) . I will have the prop back this week from the shop, I hopefully will have a better idea then. Thanks again to all..TT
WSTEFFENS posted 07-24-2002 04:31 PM ET (US)     Profile for WSTEFFENS  Send Email to WSTEFFENS     
I have a 91-25' Revenge WT W/Twin 150 Evenrudes. With light fuel & load totally trimmed up at 5500 RPM I clock in the low 50's, calculated by a Garmin GPS. Not the most happy ride but the WOT best.


lhg posted 07-24-2002 05:43 PM ET (US)     Profile for lhg    
It should be pointed out that Walt's boat does not have the speed robbing Whaler Drive, nor hardtop. From what I understand about the 25's, a pair of 150's on a notched transom will run about the same as a pair of 200's on a Whaler Drive.
Tates posted 07-24-2002 08:15 PM ET (US)     Profile for Tates  Send Email to Tates     
Well time will tell, My props are due back @ the lastest Wednesday next week. I decided to repitch them to 20 that was recommened by the prop shop & Ihg. The hub on both props were well worn,on my RH rotation the rubber liner was torn. My prop man says there are new plastic hub inserts which can easly be replaced.And wear better than the rubber sleeve,they are only $35 he suggests to carry a spare,in the event of a spun prop you could fix it on the water.Once again Thanks to all.

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