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Changing propeller size

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bayliner_50

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"I have a Bayliner 3250, with

"I have a Bayliner 3250, with 2-350 Volvo engines and Volvo outdrives that are 290...The prop on there now are 15-19, I want to put 16-23 on...Will it screw up my boat?"
 
"Terry, If you go to a 16"

"Terry, If you go to a 16" diameter you will have to stay at the pitch or lower you pitch to maintain your WOT settings, which should be 4200-4800 rpm. will a 16" prop fit a 290 drive, EL will probably know that one. also the larger diameter will slow your hole shot as you now are moveing that much more water."
 
"Terry, why do you want to ins

"Terry, why do you want to install 16 x 23 props? And what is the WOT engine RPM with the current 15 x 19 props?"
 
"Forgive guys, but IM very ver

"Forgive guys, but IM very very new to all this, what does wot mean? all I know now is that I have a 15X19 counter rotation props and my speed is 23 mph at 3500 RPM. I want to go faster and I thought bigger was better...I just bought this boat...260/290 Volvo.....I know its a big boat, but can it go faster?"
 
"Terry, the recommended maximu

"Terry, the recommended maximum RPM range for your engines is 4000-4400 RPM. If your maximum RPM is 3500, your propellers are too big and you need to go down in pitch to 15x15" or 15x17". With too large propellers you risk overloading the engines. Regarding this, you may want to go to the VP site and download the manual for your engine (select AQ260A), then read at the bottom of page 3.

http://www.volvo.com/volvopenta/global/en-gb/marineengines/operators_manual/

Also, the following link contains good information about propeller basics and propeller selection in the first 5 pages of the document:

http://www.volvo.com/volvopenta/global/en-gb/marineengines/operators_manual/"
 
"Have a look at this link:
[u

"Have a look at this link:
http://www.boat-world.com/boatads/832003978.html
That indicates a max speed of about 30 knots.

Running 15" pitch at 4400 would give around 33 knots 'nominal', 28-30 real, You are running 19" pitch! Drop 4" pitch and You have the RPM required.
If You want economy out of it, I suggest You give the 16" dia Volvo a try. They are made for diesels, huge blade area, but to my experience the best for Your combination of boat/engine."
 
"one inch of pitch change = 20

"one inch of pitch change = 200 rpm's.
if you move up in pitch you move down in rpm's
if you move down in pitch you move up in rpm's.
if you are only pushing 3500 rpm's, then move down to a 15x17. This will bring the rpm's up to at least 3900.
I had a 14x19 on my boat, and was barely getting 3000 rpm's.
moved to a 14x15, and the boat came to life.
I could actually push almost 5000 rpm's and my top speed went to 28 mph.(as it was only doing maybe 10mph before)"
 
"The 23" pitch propellers

"The 23" pitch propellers will probably burn down Your engines in an even faster 'speed' than Your present set-up.
Go DOWN to 15" if You want the engines to survive and boat to perform.
As a direct answer to Your question: The 23" props will soon slow You down to 0 knots/miles/RPM, engines gets overloaded and dies!!!!!!!!"
 
"Terry, my apologies, as the s

"Terry, my apologies, as the second link in my previous post is incorrect. The one from I suggested you should read the first 5 pages is this one:

http://www.miwheel.com/MIWheel/pdf/obsd_03.pdf

Basically, the more pitch/diameter in a propeller, the harder the engine has to work. Yours is already working too hard, as at WOT it should reach at least 4000 RPM. If you keep increasing your pitch/diameter, as Morten said very well, you will burn down your engines in no time. Try a 15x15" first, and if the engine RPM at WOT go over 4400,then you can increase the size to 15x17"."
 
"If You want the correct prop

"If You want the correct prop spec for Volvo, use this link:
http://www.volvo.com/NR/rdonlyres/2D2F5550-D247-4F3D-BE18-B8D3E71BEAA6/0/Prop_gu ide_2005_2006.pdf

Scroll down to page 14 and look at Aq 260, and You'll find both the 16" and 15" dia.
Then it is up to You to choose. Normally bigger blade area -lower pitch gices better economy, higher cruising-speed, lower planning threshold, compared to less diameter, higher pitch which gives the top end speed.
Look at the form and You'll notice that 16" at same rpm gives higher speed than 15" at same pitch. This due to less slippage. You lack min 600 rpm which is nominally 3" down on pitch and would put You in 15" x 16" which does not excist, but is covered well by the 16" prop (dia).
But note this form goes for Volvo props only, other manufacturer might have different caracteristics and performance/rpm curves."
 
"Thanks allot guys, I put on 1

"Thanks allot guys, I put on 15X19 w/cup . I think both prop were slipping. One more than the other. One was slip around 2300 and the other one around 3600. Im getting 32mph now with the changed prop with 4000 WOT. Is that about all I can get out of her?"
 
"My guess that is not Volvo pr

"My guess that is not Volvo props, and the slip percentage You have is horrendous, far tooooo high.
If possible, try to borrow 2 16 x 15 from a dealer and test! Do a fuel consuption test, and You might be shocked! The 16" will probably save You 10+% in fuel, both milage and hour."
 
"Terry, it looks to me that if

"Terry, it looks to me that if the props were slipping, the engine RPM would increase without any increase of hull speed.

According to the link posted by Morten, the maximum speed you are getting now is about right. Have you checked if the bottom hull is clean?"
 
Terry:
You might also want to

Terry:
You might also want to keep in mind that running the motors at WOT for long periods of time is hard on them and uses about 50% (or more) gas than optimal cruising speed (usually 75% of WOT). Those extra RPMS at WOT will burn MUCH more gas and only give you a few more mph... not a good trade off! Good luck!
 
"I have a 70 Chris craft XK19

"I have a 70 Chris craft XK19 with a 350 chev,425hp, and a 250 drive that is original to the boat. We are currently running a 14x19 prop and just got the boat back in the water after reworking the engine. She turns nearly 5800 rpm IF I take it to WOT. This motor is built for higher Rpms, but the boat is running 50Mph at around 4800rpm. I wonder what the best prop may be. I did find a rare 14x25, but wonder what a 15x21 would do to help eliminate slippage when we throttle up. Any ideas?"
 
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