[Public-List] Propellers

[Gordon Laco]

Hi folks - 

We motor in SURPRISE at 5kts... Fuel consumption is good at that speed, the
engine isn't too noisy, and best of all, the arithmetic required for dead
reckon is easy using a nice number like '5' for the speed.

I know there's been a ton of email traffic about props.... I've wondered
sometimes if I should make a change (we have the standard factory supplied
prop) but when I consider what other yachts put up with I stop thinking
about it.

We always seem to have more power than our friend's boats. We can motor just
about as fast (unless they are longer boats) when we have to.

The times when we've been hard pressed by weather and need power the A4 with
the standard two bladed prop has always served extremely well.  We have hove
to in squalls with all sail furled, the engine ticking along at 800rpm and
the helm locked hard over.  When we've had to tack, 1,100 rpm will push her
head around. And that in 60knts + of wind.   We have motored out of narrow
channels with loads of wind on the nose and a pitching head sea that was
putting the bow deep under water on each dive... We had power to spare.

This is beginning to sound monotonous, I'm sure, but my feeling is that with
the A4 and the standard prop the A30 is if anything, overpowered.

As John says below... Sailboats generally make rotten motorboats.
Traditional ones particularly because of the weight in the ends they carry
around in their overhangs which promotes speed-killing pitching when going
into a head sea.

So, my advice to anyone who is in a group where someone wants to motor at
7knots...  I'd say just wave good bye and let 'em go.  Maybe they'll be
buying McGregor motor-boats-with-little-masts.  I hear they do 20kts under
power....




On 14/11/11 3:13 PM, "John Riley" <jriley at dsbscience.com> wrote:

> 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
>> 
>>  
>> 
>> _______________________________________________
>> These businesses support your Association:
>> http://www.alberg30.org/store/A30supporters.html
>> Please support them.
>> _______________________________________________
>> Public-List mailing list
>> Public-List at lists.alberg30.org
>> http://lists.alberg30.org/listinfo.cgi/public-list-alberg30.org
>> 
>>   
> 



 1321302822.0