[Public-List] Propellers

[John Riley]

If your desire is to go 'fast' while motoring, a motor boat will be MUCH
better suited to the purpose.

An Alberg 30 is a sail boat.  Period.  It's not a motorboat, nor is it a
'motor sailer.'

EVERYTHING about the design of the hull is the way it is for sailing.

If you were getting 7.5 knots over ground (was there a FAVORABLE
current?), you were doing pretty darn good.  No prop is going to get you
better than hull speed...it's all about Load Waterline and wave making. 
She's not a planing hull, so there is no "faster."

I would like to hear other's comments on this, but I have found bottom
condition to be a BIG factor in boat speed (and low speed handling).  A
crusty bottom only hurts; how much it hurts may vary.

Plan to motor no faster than 5-6 knots through the water, and that not
efficiently.  My "efficient" motoring speed is about 4-4.5 knots through
the water.

John
#521, Gaelic Sea

Bart Knapp wrote:
> In the refit of our A30, it occurred to me that now would be as good a time
> as any to upgrade the propeller.  This past summer I was on an Allmand 31
> with a two bladed prop and in company with an Erickson 35 and Shannon 39.
> We were on the ICW from Galveston to Corpus and initially had the wind
> directly on the bow.  The Allmand had quite a task keeping up with the other
> two.  I know that just by size of the boat, there would be a problem, but
> with both the Erickson and Shannon throttling back, the Allmand had all it
> could do to keep within about two miles of the others - that was under full
> sail (after the wind had shifted) and the motor running.  The owner of the
> Erickson said that by changing from a two bladed to three bladed prop, the
> Allmand would have picked another knot or so.  The Allmand was pushing to
> get 5 knots over ground with motor only and was just tipping 7 - 7.5 motor
> sailing with a favorable wind direction and about a 30-35 degree heel.
>
>  
>
> Even though the A30 is currently land locked on a lake and effectively dry
> docked because of the drought, if we get it to Galveston Bay, we will then
> be able to get out to the Gulf of Mexico and the ICW.  I am looking toward
> sailing on the bay and take an occasional trip on the ICW.  Those trips may
> be in the company of other boats including the Erickson and Shannon, but
> some others that are close to the same size as the A30 and going on up in
> size.  Most of these cruises would be on conjunction with Sea Scout cruises
> as was this summer's.  I came away from the cruise this summer with the
> feeling that the Alberg would not be a good boat for the type of use we put
> boats to on the summer cruise, but it is a case of a bird in the hand - an
> A35 would be better, but..
>
>  
>
> Anyway, if I do change the prop out, what would be the size and pitch I
> would need to be looking for.  Currently it would be married up to an A4.  
>
>  
>
> Any thoughts or ideas would be helpful.
>
>  
>
> Bart Knapp
>
>  
>
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>   


-- 
John S. Riley
S/V Gaelic Sea
1972 Alberg 30 #521


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