Yep, that is probably why an over square, 13 1/2 prop was recommended to begin with.
When I bought my current boat it had a 17" prop. I suggested to the surveyor that it was too big for the opening. He said it looked fine to him so I referred him to Gerr's book. I suspect that he found it interesting reading:).
eric SV Meander
---In electricboats@yahoogroups.com, <dougmcq000@...> wrote:
Jason,
suggest you double-check clearances as Eric suggested.
According to Dave Gerr you should have at least 8-10% of prop
diameter as clearance with 15-20% recommended. This minimum
varies with RPM. The primary reason for the additional clearance is to
minimize vibration of blade tips
Doug
On Thursday, February 27, 2014 5:48 AM, "electricboats@yahoogroups.com" <electricboats@yahoogroups.com> wrote:
4 Messages
Digest #3674
1a
Propeller question: new fixed 3-blade or used kiwiprop feathering? by "Jason Taylor" leemurs72
1c
Re: Propeller question: new fixed 3-blade or used kiwiprop feather by "Jason Taylor" leemurs72
Messages
Wed Feb 26, 2014 12:19 pm (PST) . Posted by:
"Jason Taylor" leemurs72
Hello,
I am installing an Electroprop PM-20 (formerly Propulsion Marine's 5.5KW
drive) in my boat.
To get the most out of my new propulsion setup, I will need a new shaft
and prop as the old 12x8 3-blade prop just won't do and the original
22mm shaft is both not long enough and an oddball when it comes to
fitting a prop.
So, I am replacing my 22mm shaft with a 7/8" shaft and SAE 1:16 taper.
I would have preferred to fit a 1" shaft, but that would also require a
new shaft log and strut. I would rather put that money towards my
lithium batteries...
So... the issue...
The range of props available with a 7/8" bore is limited. The used
market even more so.
I have since learned of propeller reducer bushings which allow one to
fit a 1" prop on a standard 7/8" shaft.
For example, Tacoma Propeller has some here:
http://www.tacomapr opeller.com/ parts/propeller- reducer-bushings /
The prop recommended by Electropro was a 13.5x15 3-blade, but it wasn't
available in a 7/8" bore.
I could get a 12x14 3-blade for a 7/8" bore.
But I have recently been offered a old (14 years old according to the
manufacturer) Kiwiprop by another member of my yacht club.
The 16" blade set is much too big for my motor, even at the smallest
pitch setting.
This is fine since the blades are old and a bit beat up. I can replace
them with new 14.5" blades for about $380.
The propeller boss is for a 1" bore and would therefore require a
reducer bushing.
It would also require a custom-machined prop-nut -- Kiwiprops are
supplied with a custom machined nut for the appropriate bore.
The nice thing about Kiwiprops is that the pitch can be modified with
the boat in the water. Just requires an allen key, a hookah and a
bathing suit. The pitch is variable from 18-24 degrees which on a 14.5"
prop is 10" - 13" pitch.
So my decision is between:
- a new, high performance 3-blade fixed prop that fits directly to a
7/8" shaft or...
- a rebuilt 3-blade feathering prop with a reducer bushing and new blade
set.
Cost-wise, the rebuilt Kiwi will wind up a little more expensive, but
has the advantage of reduced drag under sail.
Drag on the new 12" prop will be about 50lbs at 5kts.
Drag on the Kiwiprop is much, much less.
I would like to hear feedback from electric boaters that are using or
have used a kiwiprop on their boat.
- What have been your experiences, both motoring and sailing?
- What size/pitch is the prop and what is your motor and reduction?
- Do you race? Most of my sailing in the past few years has been club
racing but I hope to change the ratio somewhat.
- Are you happy with your Kiwiprop?
- If you are no longer using the Kiwiprop, why not? Did you go to a
fixed or to another feathering prop?
I have searched the archives already and found a few hits between 2009
and 2011. Very informative. Anyone else since then?
Until a few hours ago, I was leaning heavily toward the kiwi, but now,
I'm not so sure.
I have people waiting on me for a decision and I would like to give them
one soon.
I think the factor that will decide it for me will be the feedback of
people with experience with the kiwi prop.
Cheers,
/Jason
--
Jason Taylor
--
S/V Fugu
1978 Beneteau First 30
Electroprop PM-20
I am installing an Electroprop PM-20 (formerly Propulsion Marine's 5.5KW
drive) in my boat.
To get the most out of my new propulsion setup, I will need a new shaft
and prop as the old 12x8 3-blade prop just won't do and the original
22mm shaft is both not long enough and an oddball when it comes to
fitting a prop.
So, I am replacing my 22mm shaft with a 7/8" shaft and SAE 1:16 taper.
I would have preferred to fit a 1" shaft, but that would also require a
new shaft log and strut. I would rather put that money towards my
lithium batteries...
So... the issue...
The range of props available with a 7/8" bore is limited. The used
market even more so.
I have since learned of propeller reducer bushings which allow one to
fit a 1" prop on a standard 7/8" shaft.
For example, Tacoma Propeller has some here:
http://www.tacomapr opeller.com/ parts/propeller- reducer-bushings /
The prop recommended by Electropro was a 13.5x15 3-blade, but it wasn't
available in a 7/8" bore.
I could get a 12x14 3-blade for a 7/8" bore.
But I have recently been offered a old (14 years old according to the
manufacturer) Kiwiprop by another member of my yacht club.
The 16" blade set is much too big for my motor, even at the smallest
pitch setting.
This is fine since the blades are old and a bit beat up. I can replace
them with new 14.5" blades for about $380.
The propeller boss is for a 1" bore and would therefore require a
reducer bushing.
It would also require a custom-machined prop-nut -- Kiwiprops are
supplied with a custom machined nut for the appropriate bore.
The nice thing about Kiwiprops is that the pitch can be modified with
the boat in the water. Just requires an allen key, a hookah and a
bathing suit. The pitch is variable from 18-24 degrees which on a 14.5"
prop is 10" - 13" pitch.
So my decision is between:
- a new, high performance 3-blade fixed prop that fits directly to a
7/8" shaft or...
- a rebuilt 3-blade feathering prop with a reducer bushing and new blade
set.
Cost-wise, the rebuilt Kiwi will wind up a little more expensive, but
has the advantage of reduced drag under sail.
Drag on the new 12" prop will be about 50lbs at 5kts.
Drag on the Kiwiprop is much, much less.
I would like to hear feedback from electric boaters that are using or
have used a kiwiprop on their boat.
- What have been your experiences, both motoring and sailing?
- What size/pitch is the prop and what is your motor and reduction?
- Do you race? Most of my sailing in the past few years has been club
racing but I hope to change the ratio somewhat.
- Are you happy with your Kiwiprop?
- If you are no longer using the Kiwiprop, why not? Did you go to a
fixed or to another feathering prop?
I have searched the archives already and found a few hits between 2009
and 2011. Very informative. Anyone else since then?
Until a few hours ago, I was leaning heavily toward the kiwi, but now,
I'm not so sure.
I have people waiting on me for a decision and I would like to give them
one soon.
I think the factor that will decide it for me will be the feedback of
people with experience with the kiwi prop.
Cheers,
/Jason
--
Jason Taylor
--
S/V Fugu
1978 Beneteau First 30
Electroprop PM-20
Wed Feb 26, 2014 1:11 pm (PST) . Posted by:
cirejay
You are going from a 12" prop to a 14" prop. Are you sure that you have enough clearance for the 14" prop? I ask because most sailboats have too small of a prop because there just is not enough clearance to get a proper sized one in.
BTW, I have never had a kiwi prop but do have a MaxProp (feathering like the kiwi) and love it.
eric SV Meander
BTW, I have never had a kiwi prop but do have a MaxProp (feathering like the kiwi) and love it.
eric SV Meander
Wed Feb 26, 2014 1:33 pm (PST) . Posted by:
"Jason Taylor" leemurs72
I have about 8.25" from strut center to hull which allows for about a 15" prop.
/Jason
/Jason
> On Feb 26, 2014, at 16:11, <cirejay@hotmail. com> wrote:
>
> You are going from a 12" prop to a 14" prop. Are you sure that you have enough clearance for the 14" prop? I ask because most sailboats have too small of a prop because there just is not enough clearance to get a proper sized one in.
>
>
>
> BTW, I have never had a kiwi prop but do have a MaxProp (feathering like the kiwi) and love it.
>
> eric SV Meander
>
>
Wed Feb 26, 2014 3:59 pm (PST) . Posted by:
cirejay
That being said, without commenting on the merits of the kiwi, I can't see the downside of the feathering prop.
I base this, of course, on the assumption that you will be using the boat as a sailboat and the purpose of the motor is truly auxiliary. I know that I would not want to be dragging a large 3 bladed prop around on what is essentially a racing hull.
Good luck and look forwarded to hearing how it works out.
eric SV Meander
I base this, of course, on the assumption that you will be using the boat as a sailboat and the purpose of the motor is truly auxiliary. I know that I would not want to be dragging a large 3 bladed prop around on what is essentially a racing hull.
Good luck and look forwarded to hearing how it works out.
eric SV Meander
---In electricboats@ yahoogroups. com, <jt.yahoo@ ...> wrote:
I have about 8.25" from strut center to hull which allows for about a 15" prop.
/Jason
On Feb 26, 2014, at 16:11, <cirejay@ ... mailto:cirejay@ ...> wrote:
You are going from a 12" prop to a 14" prop. Are you sure that you have enough clearance for the 14" prop? I ask because most sailboats have too small of a prop because there just is not enough clearance to get a proper sized one in.
BTW, I have never had a kiwi prop but do have a MaxProp (feathering like the kiwi) and love it.
eric SV Meander
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