Three bladed prop?

[rajhnsn]

On my trip back and forth to Florida last year, I found that my Oday 35 seemed to have difficulty moving against moderate to strong currents. I wonder if I would get better performance if I had a three bladed prop? Have any 34/35 owners changed to a 3 bladed prop? Was there much of a difference in thrust while motor sailing? Was there much more drag while sailing?

 

[Stu Jackson]

I have a fixed 3 blade on our boat, which is very similar to your underwater shape. The PO removed the 2 blade for this one. We run a 15x10, which is also known as the proverbial "dragging a bucket through the water", although we rtaced successfully from 1999 to 2006. That bucket has propelled us from 18 years in SF to up here to BC in 2016 and through the Gulf & San Juan Islands for the last four. You will undoubtedly get skippers touting their adjustable blade props, as well as the pros & cons of each. Good luck, happy choice making.

 

[jon hansen]

2 or 3 bades, the hull is only going to go prolly just shy of hull speed. that's it. subtrack the head on current speed and you will get VMG.
simple vectors.
a properly sized 2 blade and a properly sized 3 blade will push you the same speed.
the fewer the blades, the more efficient each blade is. it is the science of such.
dragging a three bladed prop is just like dragging a bucket. this is true. dragging a two bladed prop has drag as well. that said. it's when the wind is lighter that the biggest difference will be noticed. not when it's blowing twentyfive and you have loads of horsepower. so, you will prolly sail more on the lighter wind days because your VMG'g will be way better.
i sail with a two bladed 'sailing prop'. michigan wheel. braking, backing up, maneuvering, i find no difference at all between the two. i have a full keel and can put my boat where ever i want with the 'two'.

i disagree with those that claim you'll have a difference between a properly sized two or three.

 

[Davidasailor26]

2 or 3 bades, the hull is only going to go prolly just shy of hull speed. that's it. subtrack the head on current speed and you will get VMG.
simple vectors.

This. If you can’t approach hull speed with the current than a prop change may be worthwhile. If you can then changing the prop likely won’t help much. Hull speed through the water is, to a large extent, your limit. If the water is moving opposite your intended travel direction you just need to reduce your expected speed by the speed of the current.

 

[rajhnsn]

Thank you. Things to think about.

 

[jibes138]

Your prop needs to be matched to your motor to achieve the full rated max. RPM otherwise you will be either lugging the motor or underpowered. I changed from a 2 blade to three blade when I repowered the boat. I get a lot less prop walk in reverse with the three blade. In general backing the boat is much better. I can't really speak to the forward performance as it's not a fair comparison as the new motor has higher HP (25 vs 21) and two variables were changed. I have been in really strong currents where three knots at 80% full throttle is it. I am happy with the three blade but not enough difference to recommend a switch without the repower where a new prop was needed anyway.

 

[rajhnsn]

That makes sense. I think a repower is in my future so probably a good idea to do it all at once.

 

[Kings Gambit]

A prop must be free of fouling for maximum propulsion.

 

[Newport Bob]

Another possibility- if a previous owner replaced the alternator with a larger one it reduces horse power for propulsion.
I did this - replaced 60 amp with 100 amp (and external programmable regulator)
Installed an alternator cutout switch in the cockpit - completely removes the alternator load - in case I needed the horse power to power thru a foul current (also because the next year model has a larger engine possibly due to some owner complaints of under power)
Check Main Sail for great information on how to do this - that’s where I found the idea and info —- thanks Main Sail!!

 

[rajhnsn]

Yes, a previous owner had upgraded the Alternator to 120 amps. There is also an alternator shut off switch but it has not been working. I think the switch was tied to the tach but that gave up the ghost some time ago. I suspect the tach was not able to handle the higher output from the alternator. I wasn't sure why the switch was there until you suggested this. I replaced the external programmable regulator last year.