Ok Jango

[Mark Emaus]

Here is the latest for the propulsion of the boat.

As in previous post, it is a pontoon 20 foot long 8 foot wide and will weigh no more than 2,000lbs. We will be turning 53 hp at a optimum range of 1800 to 2400 rpm
What do you recommend for a prop size and pitch for this scenario? Now if we increase the rpm to 4,000, what would you recommend? The reason for the rpm at these speeds is what our Hydraulic motor will turn. The 4,000 would be if we gear the hyd. motor before it gets to the prop shaft.
As always….thank you for your expertise!

Mark

[Jango]

Mark,
2000# w. 53Hp @ 2400 RPM would require a 13x13, 3 bladed prop, 24mph w.17% slip

2000# w. 53Hp @ 4000 RPM, a 10x8, 3 bladed prop, also 24 mph w. 17% slip

[Mark Emaus]

Originally Posted by Jango

Mark,
2000# w. 53Hp @ 2400 RPM would require a 13x13, 3 bladed prop, 24mph w.17% slip

2000# w. 53Hp @ 4000 RPM, a 10x8, 3 bladed prop, also 24 mph w. 17% slip

You are the man JANGO!

Tell me....what does the slip really mean? At high speed you lose 17 percent of it performance?

Mark

[Mark Emaus]

JANGO,
One more thing. Looking at what is avaiable, 13x13 is not.
Here are my options.....14 x 11, 14 x 13, 13x21 cupped , 13x19 cupped, 13x17cupped 13.25 x 15 cupped, 12 5/8 x 21 cupped,
next group
12.25 x 15, 12.25 x 9, 11.75 x 17, 12 x 11,
I would either need to have one group or the other for shaft compliance. Which group would you think would be best for the 53 hp stats?
I am thinking of the first group???

thanks

Mark

[terhohalme]

Upload a simple software here and you can be almost as the man.

http://www.castlemarine.co.uk/pitch.htm

[Jango]

Mark,

If 53HP is available at 2100 - 2200 RPM, The 14x13 should work fine, otherwise use the 14x11 with slightly less speed.

Slip is the amount of Lost motion, compared to the Ideal of 13 inches per revolution (ZERO SLIP). In reality NO prop can achieve 100% or 13in. of movement, with a 13 pitch prop.

6% slip is about the best posible and only with very high speeds. As speeds increase, slip CAN go down

The Prop on my 87 mph Inboard Runabout has about 7% slip

[Mark Emaus]

thank you JANGO.....

MARK