Typical Propeller Sizes for Sail and motor boats

Hi

I have a general question, could you let me know typical sizes of propellers on a sliding scale for motor and sail boats (if different). For example, starting at 2.5m (8ft) boat the general increase in size per 1 metre or sensible next size up.

thank you in advance

Nick

 

The propeller size is proportional to displacement, type of hull, engine power and expected use of boat. You need to narrow the question.

 

This is a bit like - "how long is a piece of string?"

It might help if you explain you reason for asking the question so you get a better directed answer.

For the boats I build I am after best possible efficiency. The power input is small and the hull reasonably easily driven. The typical prop I use is 16 X 26. A very unusual size and shape.

Generally props are sized for what fits. Typically only something like a tug has the boat built around the prop/s.

For best efficiency you go for the largest diameter that will practically fit and use the lowest blade area ratio that provides blades heavy enough to withstand the loads.

As the speed goes up cavitation becomes an issue to contend with. At very high speed a surface piecing prop will get the best result.

Rick W

 

Hi Rick/Gonzo

Thanks for your reply...

Its a general marketing question really... We have produced an anti barnacle grease which is for a Prop and shaft and was looking for a guide as to typical prop sizes. I know its a bit vague, given most props are based on the engine capacity, but its just a sliding scale of prop sizes really; for typical sail boat, yacht and motor boats. Any steer would be good.

Many thanks

Nick

 

Take this as a rough guide.

Small props for dinghies and small runabouts say 7 to 10".

Up to midsize trailerable runabouts and small, easily driven yachts 10" to 16".

Large trailerable, semi-displacement cruisers and larger yachts 16 to 20".

Above 20" you are getting into the larger permanently moored craft and work boats.

Rick W

 

Great thanks Rick,

I'll send you a sample when its ready to go, if you'd like?

Cheers

Nick

 

It sounds interesting. Do you just rub it on?

 

nstaylor,

The current "best" antifouling for moored vessels here seems to be Propspeed, yellow clear finish and sticky like silicone rubber.

Many old fistermen here also used Lanoline grease and STP (oil additive)....let us know if your product works better than those and we can certainly market it for you here.

 

Lanoline grease and STP will cause a sheen and discoloration in the water. That is a violation of the lLaw in most countries. I don't think you could market that without ending up with at least a huge fine.

 

propeller selection are affected by several factors of ship geometry and hydrodynamic behavior such:
speed,wake,drag,disp., LWL etc.....

 

propeller selection are affected by several factors of ship geometry and hydrodynamic behavior such:
speed,wake,drag,disp., LWL etc.....

 

Propeller for sailboat, 3-blade:
Diameter=0.04*LWL
Pitch=(0.5...0.6)*Diameter
This is rough guidlene that works for most of sailboats.

 

"Propeller for sailboat, 3-blade:"

That's not a propeller its a SPEED BRAKE!

A proper sized 2 blade will give the same propulsion under power and less drag underway.

FF

 

3 blade - can be feathering/folding... Fixed 3 blade prop is acceptable for most of cruising boats.

2 blade - good option for racer or racer-cruiser with small engine.

An in case if we need to increase DAR to avoid cavitation, there is no alternative to 3 blade prop.