1997 Searay 240DA prop

[lilpint]

Hey, love the forum lot of great information. I am hoping I might be able to get some insight on the best prop for my boat. The boat was bought with a 16"x16P prop, with great hole shot but very fast when trying to dock. I had the original prop 15"x17P and its great at docking, but with more than 4 people on board its hard to get the boat to plane out. The boat is on Lake Norman in NC so water conditions are fairly calm. The 16x16P has damage on it from the original owner so I have to buy another prop and wanted to get some opinions on what to do. Thanks in advance for any help.

1) Performance issue you are trying to correct.
Best for 4 - 6 passengers but something that can be managed in tight docking situations.

2) Current prop
15"x17P Aluminum not sure of manufacture.

4) RPM Information
4800 WOT
4000 RPM with 15x17P 28 - 30 Knots
4000 RPM with 16x16P 33 - 36 Knots
600 - 800 RPM 16x16P 4 - 5 KNOTS (GPS verified)
600 - 800 RPM 15x17P 2 - 3 Knots (GPS verified)


5) Engine
5.7 MerCrusiser Alpha One (1997) 250HP

6) Boat make model
1997 Sea Ray Sundancer 240 24'

 

[hwsiii]

Re: 1997 Searay 240DA prop

Lil, theoretically you want a prop with very low prop slip to get the most thrust and speed possible out of your prop. I doubt very seriously you are willing to trade the extra 6 MPH cruising speed for a slow docking speed, although I could be wrong. I don't really believe these numbers are exactly right but I do believe they are to the best of your recollection, as they are a range rather than exact numbers.
Your 16" prop has a much lower prop slip than your 17" so it is definitely giving you much better performance, and that includes idle speed as well. In my opinion I would keep the 16" pitch and learn to slide the motor in and out of gear when you are docking. I had a 43' with the same problem at idling speeds and that is the way I handled it. I would buy another 16 x16" pitch. Here are your numbers for prop slip.

Prop Slip

Hope this helps.

H

 

[lilpint]

Re: 1997 Searay 240DA prop

Thanks, the information is very helpful. Regarding the numbers I did express the MPH in Knots (first boat with a speedometer). Now I am starting to understand how the Pitch and slip works. So based on the numbers the 16P looks great.

Now how does the size of the prop affect everything. I am going from a 15" to a 16" prop, how does that affect everything?

 

[hwsiii]

Re: 1997 Searay 240DA prop

Do you mean pitch? You already have a 16" diameter with a 16" pitch.


H

 

[lilpint]

Re: 1997 Searay 240DA prop

Sorry the prop installed is 15"x17P, the 16"x16P was damaged. So 16P is the right choice, or maybe I will research other Pitches, now I am trying to determine if I should get a 15x16 (may not be a valid prop), versus a 16"x16P.

Thanks.

 

[hwsiii]

Re: 1997 Searay 240DA prop

What is your wide open throttle RPM and speed.


H

 

[lilpint]

Re: 1997 Searay 240DA prop

4800RPM Is the max from Sea Ray.

 

[hwsiii]

Re: 1997 Searay 240DA prop

What RPM are YOU able to turn with your boat.


H

 

[lilpint]

Re: 1997 Searay 240DA prop

I can go to 4900 - 5000. That's max, if you need to know, I run the boat around 4000 for running on the water. Thanks.

 

[hwsiii]

Re: 1997 Searay 240DA prop

I just wanted to know would it reach maximum WOT RPM.


H

 

[lilpint]

Re: 1997 Searay 240DA prop

Great, so what does change when you increase the size of the prop diameter wise versus pitch?

 

[hwsiii]

Re: 1997 Searay 240DA prop

When you have that much change in diameter it is usually accompanied by a change in blade geometry which can have major impacts on RPM and speed. In this particular case you are going to lose blade surface area and have a commensurate increase in prop slip and loss of speed.


H