Hi Carl,
My change to 1" shaft was not a big deal, small expense in the scheme
of repower. No change to strut except new cutlass bearing (required
anyhow). Kiwiprop recommended the size & pitch. Pitch is no big deal
since it's easily adjustable, unlike a Maxprop.
It looks like their smallest diameter is 14.5". You nailed the hub
vs. tip location relationship that allows a larger diameter prop. It
also helps that our hull sweeps up nicely in that area, so any gain
aft equals big rewards.
http://www.kiwiprops.co.nz/cms/index.php/therange/kfp-composite-stainless
Cheers, Russ
Sweet 35 mk-1
the following message on the subject was sent to the list last June:
I changed the prop shaft from 7/8' to 1" diameter. And changed the
location of the prop taper so it overhangs (aft) the cutlass bearing
a bit more to get the tip clearance. (Reminding you that when you
change an engine type, the output flange may not be in the same
location as the A4.)
The strut and location is original. A new cutlass bearing is
available with the same shell O.D. and a 1" prop shaft I.D.
I put in a "running take out" Yanmar 2QM20 which is a old style
brute of an industrial type engine. Long stroke (for good torque)
and slower RPM than modern but far too tall for the 35 mk-1. The
Kiwi-prop people calculated I could swing a 17 1/2" wheel.
I went with 16" because I wanted to get a Kubota block engine in
there eventually. The Kubota is a higher RPM engine. In Yanmar it
would be closer in comparison to 3GM series.
As Dennis mentions the max diameter swing plane is important. A
folding & feathering prop tend to have a hub which places the blades
further aft than a fixed prop. The Kiwi-prop tips are the furthest
aft of any prop that I have seen.
In summary, same strut & location, 14" folder will be no problem,
suggest 1" prop shaft to handle extra torque, go for low-profile engine.
Cheers, Russ
BTW, I found my Kubota engine, an old Universal diesel 25 HP and
it's sitting in my shop awaiting install.... but the Yanmar keeps
running and now it's summertime!
At 06:59 AM 09/11/2014, you wrote:
Having searched the archives and not found this info, I feel the
need to ask...
I am committed to a re-power this winter and am surprised at the
difficulty in choosing an appropriate prop which then leads to the
appropriate engine HP and transmission choices. I already have input
from two other 35-1 owners but am looking for a wider array of
input. My old engine/tranny/prop is the venerable Atomic-4, 1:1
tranny, 12x6 folding prop. The new engine will be a BetaMarine...
but either 20 or 25 HP depending on how much power a prop that FITS
can absorb through a choice of a 1.45:1, 2:1, or 2.6:1 transmission.
As I really don't want to face the added expense of upsizing the
shaft from 7/8" to 1" (even a 14" prop can be safely driven on a
7/8" Aquamet shaft) or worse - moving and replacing the strut to
gain prop diameter - please provide whatever real-world info you
have on the prop (make, diameter, pitch); engine HP, and
transmission ratio that you are using on your 35-1.
It turns out that the prop make/model is critical due to the
effective hub length. For instance, my current folder places the
blades 5 5/8" behind the strut (5" hub, with 5/8" exposed shaft).
The prop I am considering (Flexofold 13") has only a 4.5" hub
length, while a Martec 14" appears to be a beefy 9" from hub to
blade pivot. So the length of the hub has a large effect on tip
clearance. As Dave Gerr (The Propellor Handbook) recommends an
absolute minimum of 10% clearance (a 14" prop thus needs 7" + 1.4"
clearance from shaft center to hull) - I only have 8" clearance with
a 4.5" hub) - a longer prop hub allows for greater prop diameter (a
very good thing). So real-world experience - including your
experience with speed, prop noise, and vibration from using a small
blade tip to hull clearance would be invaluable to me.
The problem is complex enough that Flexofold actually refused to
recommend a prop, tranny drive ratio, and HP requirement; and
recommended that I work with a boat-builder to work out these choices.
Your actual numbers and knowledge will be greatly appreciated.
Thanks,
Carl Gerstle
Impulse
C&C 35-1 #149
Portsmouth, RI
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