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BigBone posted 12-03-2001 11:12 PM ET (US)   Profile for BigBone   Send Email to BigBone  
I recently had to come home on one motor and noted the remaining motor struggled to keep the boat on a plane. I normally run twin 225's turning 21" pitch props with a top speed of 54-57mph. I believe that I should be able to cruise around 30mph and comfortably stay on plane if correctly propped. With that in mind, I decided to buy a spare set of props just in case I ever need to make a long run home on one.

Coming down in pitch from the stock 13.75x21, I tried a 14.5x17. The boat still struggled to get on a plane and the prop seemed to ventilate quite a bit. Also, though full RPM (5500) was attained, max speed was only around 35mph, indicating a great deal of slip. If I backed the throttle to 4700rpm, the boat slowed to 25 and would have come off plane with any seas.

I then tried a 15.25x15 and liked the performance with a very light load, about 38.5mph at 5500rpm. Sadly, when I loaded the boat, I again experienced the same struggle to plane and could barely make 25mph and could not plane in 3 foot seas.

What's the answer? Less pitch and more diameter...that may not be possible. Four blades? I find it hard to believe that a boat that can go mid 50's cannot plane comfortably on one. Help!

bubba18 posted 12-03-2001 11:25 PM ET (US)     Profile for bubba18  Send Email to bubba18     
Where both engine in the water. Can you raise one without bringing up the other. The lower end of the motor is a HUGH anchor, that drag would keep you from running in the area that you think.
lhg posted 12-04-2001 01:22 AM ET (US)     Profile for lhg    
It sounds like your engines may be mounted too high, which is often done for most efficient speed, but not the best for the single engine situation you are describing.

Assuming first that the other engine was tilted clear, if your spare prop is of different design than the main props, it could also slip more, particularly if elevated.

What kind of 225 went out on you? An Optimax or Ficht, perhaps?

BigBone posted 12-04-2001 06:54 PM ET (US)     Profile for BigBone  Send Email to BigBone     
Bubba: Yes, the other is tilted clear.
IHG: The motors used to be higher, but are now mounted appropriately. They are Yamaha's, but no complaints, I run em' real hard and at over 1000 hours, I'm glad the powerhead went since it's still under warranty!!

I just want to be able to cruise at 27 or so on one...why should that be so difficult on a boat that'll do 57 on two? Help!

John from Madison CT posted 12-04-2001 07:10 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     
I remember that my 25' Whaler, which had a tower and twin 150hp Sea-Drives (yes..I know ...I know.. they were awful) was able to plane on one motor.

The boat topped out at ~40 knots with 2 motors and probably at least 20 with one motor.

John

bigz posted 12-05-2001 05:39 AM ET (US)     Profile for bigz    
What boat are you running these 225's on?

I don't think it was mentioned!

Clark Roberts posted 12-05-2001 12:18 PM ET (US)     Profile for Clark Roberts  Send Email to Clark Roberts     
My friend's 23 Conquest has twin 135 Merc Opti's and runs about 48mph at WOT and 5600rpm on non-vented Quicksilver Mirage Plus 17"pitch props. With one engine tilted clear it will plane effortlessly and run about 25-28mph. Happy Whalin'... clark... Spruce Creek Navy
BigBone posted 12-11-2001 01:25 AM ET (US)     Profile for BigBone  Send Email to BigBone     
BigZ...

Not sure I can specify the boat type since it is not a BW!

Actually, it is a 1998 Contender 25 Open. I tried a a 4-blade 15 x 16 which did not work well at all and then a 15.5 x 15 stainless this weekend and it worked the best so far but still ventilates too much especially in any seas. I think a 16 x 14 or 16.25 x 13 might work well if they exist.

The 15.5 diameter clears by about 3/4", but how close is too close to the cavitation plate?

Bigshot posted 12-11-2001 10:03 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Honestly....when it hits.

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