[Public-List] Prop Size Discussion

Wed Mar 24 15:45:23 PDT 2021

Richard
  My beta 16 is installed with the TMC 40 gear at 2:1 ratio.  I still have
the 13x7 2-blade prop. The engine tops out at about 3600 rpm, spins the
prop at 1800. This is where my Atomic 4 drove the same prop and gave me 6.5
knots calm water, clean bottom. Based on the power -rpm curve for the A4
this was just about 16 hp, so I was pretty confident I could use the same
prop.  It uses a lot less fuel than the Atomic 4.  I have been in 20 knots
head seas with 3 foot waves - nasty  Chesapeake bay 30 foot long waves- and
kept up 4.5 knots .

I have neither heard or seen any evidence of cavitation .

Regards
Mike
Rinn Duin 272
On Wed, Mar 24, 2021 at 17:19 RICHARD HAZLEGROVE via Public-List <
public-list at lists.alberg30.org> wrote:

> In the prop discussion from February I noted a comment from Mike on Rinn
> Duin 272 regarding his Beta 16 diesel conversion.  I am considering the
> same engine and would love to hear back from Mike with a few details such
> as his transmission reduction ratio, prop size and performance in clear
> water and in wind and chop.  I have heard great things about these engines
> and would like to learn of his experience in our Albergs.
>
> By the way, I currently have a little BMW 12 hp diesel that has been good
> over the years but parts have gotten hard to come by.  It has a lot of
> torque and a 2.7 to 1 reduction gear spinning a 13”x14” three bladed prop.
> It will approach 6 kts with a clean wheel and bottom but less than half
> that in strong headwinds/chop.  The 13” prop may be a little tight in the
> aperture but I only hear/feel cavitation when running hard at full rpm’s
> into strong headwinds.
>
> Richard Hazlegrove
> Quest 433
> Mobjack Bay, VA
>
> > On Mar 24, 2021, at 4:05 PM, public-list-request at lists.alberg30.org
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> >   1. Re: Prop Size (scott at scottmaury.com)
> >
> >
> > ----------------------------------------------------------------------
> >
> > Message: 1
> > Date: Wed, 24 Mar 2021 14:40:52 -0500
> > From: scott at scottmaury.com
> > To: Alberg 30 Public List -- open to all
> >    <public-list at lists.alberg30.org>
> > Subject: Re: [Public-List] Prop Size
> > Message-ID:
> >    <20210324144053.Horde.DkBOojFrjFIqlYi_ChxyXk9 at gator2001.hostgator.com
> >
> > Content-Type: text/plain; charset=utf-8; format=flowed; DelSp=Yes
> >
> > hey just a follow up, Michigan wheel has recommended that I get a 12"
> > / 11  three blade prop and that is what the engine guys have ordered
> > for the Bill of Rights
> >
> > Thank you all for your response, I'll follow up with this further
> > after some use this summer.
> >
> > Scott
> >
> >
> > Quoting John Johnston via Public-List <public-list at lists.alberg30.org>:
> >
> >> Regarding prop size- My Alberg 30 ( # 69) spent many more months at
> >> the slip this past year unattended than I had anticipated. Last
> >> October I came down to the Bay from my home in Massachusetts
> >> intending to spend a pleasant month sailing. It turned out that
> >> while the diesel fired right up, I had no forward or reverse motion.
> >> The shaft was turning, but no motion. I thought perhaps it was
> >> barnacles on the prop, and I hired a diver to give it a scrape and a
> >> scrub, but he resurfaced in a minute and informed me that I had no
> >> prop, just a hub. Severe galvanic corrosion. The story goes on, but
> >> the point is that I am looking to buy a new prop.
> >>       My diesel is a Westerbeke 20 2B. Not the original engine, but
> >> when a previous owner installed it they kept the 2 blade prop that
> >> was appropriate for the Atomic 4. I decided to upgrade to a three
> >> blade Chesapeake prop at that time,  (5 years ago) which was deemed
> >> to be the proper, well, prop, for the new engine and transmission.
> >>      However, now it is time for a new prop. What I had bought was
> >> a 13x12x3 from Miller Island. Lovely piece of work, but it is shot.
> >> I have also been doing some research and reading, and came across an
> >> article about prop size by Ted Brewer more than a decade ago, and he
> >> maintains that the prop in an aperture should never have less than
> >> two inches of clearance at the top of the blade, to avoid
> >> cavitation. The aperture height on my Alberg is 14?. To achieve that
> >> 2? would be a 10? prop, which seems awfully sleight. I am thinking
> >> perhaps an 11? prop with whatever adjustment to pitch would be
> >> appropriate. Or maybe 12? as a compromise.
> >>     I would very much welcome the wisdom of the elders, and
> >> everyone else that has expertise or experience  with this matter.
> >>     Thanks to anyone offering their experience or advice
> >>
> >>> On Feb 24, 2021, at 7:41 AM, Mike Meinhold via Public-List
> >>> <public-list at lists.alberg30.org> wrote:
> >>>
> >>> ?Scott
> >>> I am glad to hear Bill of Rights will be sailing again.
> >>>
> >>> If you have some specs on the Vetus 25 we can see how it compares with
> the
> >>> A4 -13x7 2-blade match that you most likely have
> >>>
> >>> I repowered with a beta 16 and kept the same prop as I found it was
> about
> >>> the same operating point
> >>> We would need the engine torque and power vs rpm, and the gear ratio to
> >>> check.
> >>>
> >>> For the sails I suggest you provide the sailmaker with  the Chesapeake
> >>> Alberg rules in the Association handbook.   I highly recommend 2 reefs
> and
> >>> use both frequently.
> >>>
> >>> Mike
> >>> Rinn Duin 272
> >>>> On Tue, Feb 23, 2021 at 21:26 Bill of Rights #487 via Public-List <
> >>>> public-list at lists.alberg30.org> wrote:
> >>>>
> >>>>
> >>>> Hello everyone, I am a long time A30 owner and also had a Tartan 34-2
> >>>> for 10 years, I just recently sold that boat.
> >>>>
> >>>> I'm putting all my efforts back into #487 "Bill of Rights" this year!
> Yea!
> >>>>
> >>>> I am re-powering to a 25HP Vetus engine with a 2:1 hearth gear and
> >>>> just wanted to hear what others have "sized" for a 2 blade sailor prop
> >>>> on other diesel conversions?
> >>>>
> >>>> The At-4 engine was rebuilt and has less than 10 hrs.   Any interested
> >>>> parties should reach out to me
> >>>>
> >>>> I'm also getting a new suit of sails from Precision, #400 series! Does
> >>>> anyone have any experience or suggestions would be helpful  Main w/ 2
> >>>> reefs,   135# headsail w luff  ??????????
> >>>>
> >>>> New interior cushions!
> >>>>
> >>>> Boat still has some deck issues and I'll have to fix that as I go
> >>>>
> >>>> Hope to catch up with like-minded a-30 sailors this summer on the bay.
> >>>> I am securing a slip on the Magothy River so I'll be closer to my home
> >>>> and sail some new waters this summer!
> >>>>
> >>>> Thanks   Scott
> >>>>
> >>>>
> >>>>
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