[Alberg30] 2 blade prop

[Kevin Blanc]

We're using the 3x10x7.4 prop sold by Indigo Electronics 
(www.atomic4.com). It's (advertised as being) designed specifically for 
the A4 engine. Since all that Indigo does is A4 stuff, I don't  think 
that's hype. It's an oddly shaped prop with little winglets on it that 
are meant to cut down on cavitation.

It's much better backing. It backs straighter, steers a little better, 
and starts moving backwards sooner.

It vibrates less.

It provides a slightly lower idle speed and, I think,a higher high 
speed. That's a seat of the pants thing, though, I can't prove it.

Boat speed recovers faster after banging into chop. This is a seat of 
the pants thing that I'm sure about.

The engine runs at a higher RPM, but more quietly (less "boom"). Some 
folks contend that that's worse for an older engine, but I don't see 
how. There's less pressure on everything inside the engine if it's 
running faster per knot of forward motion. Of course, I wouldn't spin 
much faster than 2500 even if I could. It cruises at about 2K or 2.1K. I 
would imagine that the increased water flow and charging current are 
bonuses, too, but again, I can't measure that.

All that being said, my partner is getting itchy to put the two-blade 
back on because he's concerned the prop is slowing us down when racing. 
Of course, he's right. How much, I'm not sure, but it does have slightly 
more surface area (less than 10 percent more, I think) than the original 
Columbia 13x7, and you can't tuck it behind the deadwood. Once we get 
better at racing (there's so many other things to improve at), I'm sure 
it'll come off.

If you sail no matter the wind speed, think twice. If, however, you find 
yourself motoring a lot and sailing when the wind is reasonable, you 
might like it.


Mary & Bill Mahony wrote:

>Kevin--Curious, because I'm pondering this myself.  When you say noticeably
>better, could you elaborate?  I've read the 3-blade makes a difference
>particularly in regards to backing--do you find this to be the case?
>
>Thanks for your time,
>
>Bill
>#276 "Mary Ann"
>
>
>----- Original Message -----
>From: "Kevin Blanc" <t.k.blanc at att.net>
>To: "Alberg 30 public list" <public-list at alberg30.org>
>Sent: Thursday, April 10, 2003 5:14 PM
>Subject: Re: [Alberg30] 2 blade prop
>
>
>>George, in my opinion, it's better with a three-blade. Not a panacea,
>>but noticeably better.
>>
>>George Dinwiddie wrote:
>>
>>>Yves,
>>>
>>>I would keep the old 2 blade.  In fact, I've done so.  The fact is,
>>>when in reverse you've effectively got a large fixed rudder and a
>>>small moveable keel, because the waterflow is reversed.  No prop is
>>>going to change that.  Instead, you should learn how to use what
>>>you've got.
>>>
>>>To make the boat turn well, you need water flowing past the rudder,
>>>and that means the boat has to be moving.  Going forward, you can
>>>motor slowly and the prop will add to the water flow.  In reverse, you
>>>need to be moving faster, so give it a good jolt of gas.
>>>
>>>Then, you don't want to be going too fast, so shift to neutral and let
>>>the boat's momentum carry you.  In fact, I like to give a smaller
>>>burst of forward, but not enough to slow the boat down.  It seems to
>>>help the waterflow across the rudder.
>>>
>>>It works, but because of the prop walk, you'll find the boat wants to
>>>turn in one direction (bow to starboard, stern to port).  Use that,
>>>and choose to turn that way, even if you have to turn further.
>>>
>>> - George
>>>
>>>Yves Parenteau wrote:
>>>
>>>>I'm a first time boat owner and just wondering if I should replace the
>>>>
>2
>
>>>>blade prop for a 3 blade right away before the boat hits the water.
>>>>It's a
>>>>$600 dollars expense I could do without right now. any comments
>>>>please( I
>>>>concern about reverse capabilities )
>>>>
>>>
>>
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>
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 |                This Old Boat by Don Casey                     |
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