Correct propeller

[buba]

I am wishing to install a 15 HP outboard motor on a 29 feet fiberglass sailboat.

Could anybody inform me on which should be the correct propeller dimentioning for it?

Thank´s

buba

[Tim Dunn]

Ask the manufacturer, before you buy the motor, if you haven't already. Get a long-shaft--the prop will lift out of the water when pitching in a swell if you don't. Tell the manufacturer the boat's displacement, too. Get a swing up mount, if you don't have one.

[buba]

Could anybody answer this simple question?

"which should be the correct propeller dimentioning for it?"

Please don´t tell me to ask the manufacturer NOR to get a long shaft NOR to install a swing up mount. Just the answer to the question I am asking.

Thank´s

buba

[duluthboats]

If it was simple I’m sure you wouldn’t be asking. Most manufactures have charts to help as a guide. Without this guidance it would help to know your boats displacement, and the motors operating RPM. Then I could make a respectable guess.

Gary

[CDBarry]

I tend to choose the pitch and diameter that allows the engine to acheive full RPM at very low speed, but otherwise you may want to maximize either speed or low end thrust, depending.

[mmd]

Buba, with all due respect, answering that question is what several of us here get paid to do. We ask detailed questions like, "What is the displacement of the boat?", and, "What is the length, breadth, and depth of the boat?", and, "Do you have a linesplan of the boat?", and, "What is the available hosepower and RPM?". Then we go through a whole bunch of calculations to determine the drag on the boat as it moves through the water, including wetted surface drage, appendage drag, wave-making drag, etc. When we have a handle on how much power it takes to move the boat through the water at various speeds, we then do a bunch more calculations to determine what are the optimum propeller parameters for the given set of conditions, which include type of service, expected speed, available horsepower, RPM, etc. With this data available, we then review available information from various prop manufacturers to select the prop configuration that most closely matches our theoretically optimum prop.

Or, if it is a no-brainer stock boat with stock outboard, we call the manufacturer and ask them to reccommend a prop for the application based on their experience with possibly thousands of other similar installations.

Sometimes a simple question doesn't have a simple answer.

[terhohalme]

Hello buba, if you want a simple answer, just pick up the largest diameter and the lowest pitch there is as a standard propeller for that outboard. It woun't be the optimum, but the best you can get easy. The maximum speed should be somewhere 6.5 - 7 knots.

Check this guy's website there is an easy to use program for free
to calculate the propeller

kind regards

www.fernandocarvalho.cjb.net