Changing from a three blade to a two blade prop.

basic

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I have done it at last. Been considering it for a long time now but having seen a new prop of the correct size on ebay for £80.00 I took the plunge. It had to be worth a try compared to the price of a feathering prop.
I was so tired of draging around that 16'' three blade that when I saw a 16'' two blade of the same pitch I snapped it up. Had always thought that she was overpitched at 13'' but everyone said that a two blade prop on my long keel Barbican 33 was not a good idea as it would lead to excessive vibration and loss of power. Anyway following my hunch I have done it. There is a noticable increase in speed especially in light winds and performance under power is improved as the engine attains better rpm now and no increase in vibration. Manouvering in marinas is easier as can approach the pontoon at slower speed.
I know it's against the perceived wisdom but it is a definate improvement. Just thought I would post this incase anyone else is toying with the same idea.
 

cmedsailor

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Better performance under power as the engine attains better rpm and better manouvering in marinas means you are not comparing like with like. It's a comparison of a wrong size 3-blade prop with a correct size 2-blade prop. In flat sea motoring with a 2-blade prop is supposed to be more efficient (though I have never noticed it myself after changing to 3 blades). But motoring against heavy seas and especially manouvering in marinas, with the correct size 3 blade prop, is much better. For sailing in light winds, well forget it....
 

basic

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Better performance under power as the engine attains better rpm and better manouvering in marinas means you are not comparing like with like. It's a comparison of a wrong size 3-blade prop with a correct size 2-blade prop. In flat sea motoring with a 2-blade prop is supposed to be more efficient (though I have never noticed it myself after changing to 3 blades). But motoring against heavy seas and especially manouvering in marinas, with the correct size 3 blade prop, is much better. For sailing in light winds, well forget it....

I thought that was exactly what I said. The prop was overpitched and changing to a two blade of the same pitch corrected that by allowing the engine to attain its proper rpm. The boat sails better with the two blade prop. I have all the power I need in a marina with better low rpm manouverability, As for motoring against heavy seas as my friends would tell you I sail my boat in all weathers. If i wanted to motor-sail I would buy a motor-sailer I guess it just depends if your priority is sailing or motoring.
 
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Snowgoose-1

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I would guess that your sailing performance has improved too. Are the two blades now hidden behind the deadwood ? .
 

snooks

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As for motoring against heavy seas as my friends would tell you I sail my boat in all weathers. If i wanted to motor-sail I would buy a motor-sailer I guess it just depends if your priority is sailing or motoring.

It depends on how uncomfortable you want to be for how long, or how long you want to be beating away from a leeshore to clear a headland.

My boats is a sailing boat and I'll happily stick the engine to help me get to windward in a shorter time to make things more comfortable, or to make a tidal gate, or to make last orders at the bar or all of the above :0)
 

Tranona

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I thought that was exactly what I said. The prop was overpitched and changing to a two blade of the same pitch corrected that by allowing the engine to attain its proper rpm. The boat sails better with the two blade prop. I have all the power I need in a marina with better low rpm manouverability, As for motoring against heavy seas as my friends would tell you I sail my boat in all weathers. If i wanted to motor-sail I would buy a motor-sailer I guess it just depends if your priority is sailing or motoring.

Now you have enjoyed the benefits of a correctly pitched prop you might save your pennies and get a Featherstream 3 blade with the correct pitch. Better motoring performance than either of your props and less drag under sail than your 2 blade fixed.
 

basic

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Now you have enjoyed the benefits of a correctly pitched prop you might save your pennies and get a Featherstream 3 blade with the correct pitch. Better motoring performance than either of your props and less drag under sail than your 2 blade fixed.

I would of course fit a featherstream if I had the money to spare but I dont so for me the two blade is the next best alternative.
 

Seajet

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Seems an excellent move to me Basic, if I inherited a boat with a 3 blade I'd instantly be looking around for a 2.

Can you mark the shaft so as to hide the prop when sailing ?
 

basic

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I would guess that your sailing performance has improved too. Are the two blades now hidden behind the deadwood ? .

Sailing performance much improved. I marked shaft but engaging reverse gear does not quite align the prop with deadwood. However I understand latest tank testing recommends allowing the prop to rotate for minimum drag. Have tried both with no noticable difference.
 

basic

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Seems an excellent move to me Basic, if I inherited a boat with a 3 blade I'd instantly be looking around for a 2.

Can you mark the shaft so as to hide the prop when sailing ?
I marked shaft but engaging reverse gear does not quite align the prop with deadwood. However I understand latest tank testing recommends allowing the prop to rotate for minimum drag. Have tried both with no noticable difference.
 

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