I need Propeller and or engine help

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narfi
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Re: I need Propeller and or engine help

Post by narfi » Mon Aug 03, 2020 12:44 am

Just to verify,
Aluminum you would do 12.25-12.75 diameter and 16 inch pitch.

Stainless you would do 12.25-12.75 diameter and 18 inch pitch?



CatfishHunter
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Re: I need Propeller and or engine help

Post by CatfishHunter » Mon Aug 03, 2020 6:07 am

i'm running a 3 blade 15p ss and getting 5k on my 60 command thrust, on my xf20. i had a 4 blade cupped powertech 15p and was only getting 4500. i think i need a 12p 4 blade ss to get where i need to be. i tried an aluminum 4 blade in the same pitch and lost 500 rpms. i've been on the prop hunt for months, tired of swapping and wasting money. lol hope this helps.

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cape man
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Re: I need Propeller and or engine help

Post by cape man » Mon Aug 03, 2020 6:28 am

Aluminum flexes at high rpms so you need a higher pitch than stainless, not lower. You will get about 200-300 rpms per inch of pitch reduced, so if you want to get close to 6000 rpms at WOT you will need to go more than the 3 inches recommended. 6000 - 3700 = 2300. Your current prop is way too much so the motor is bogging down, thus you'll probably get more than 300 rpms for the first inches you reduce the pitch. I fear you will be disappointed if you only drop it to an 18 inch pitch, and more importantly aluminum needs more pitch, not less.

Tom's calculations work to an extant, but you have real world numbers to work with. Talk to the prop retailer or manufacturer before you decide. Another suggestion is to buy an aluminum that you think is close (I still "guess" it will be a 14 or 15") run it and see, and then dial in a stainless. Keep the aluminium on board as a spare.

Finally, don't know if you can do it in Anchorage, but here you can try a prop and exchange it if it isn't right.
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TomW1
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Re: I need Propeller and or engine help

Post by TomW1 » Mon Aug 03, 2020 12:08 pm

Narfi yes.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Fuzz
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Re: I need Propeller and or engine help

Post by Fuzz » Mon Aug 03, 2020 12:51 pm

I know getting stuff there can be a little tough. Is there anyone there who has a 50-60 hp motor that you can borrow a prop from for testing? Anything from a 10-15 pitch would give you more info to work from. I think some other brands will fit your Merc.
When I first ran my dory the motor was way too low and too much prop pitch. Took a little testing and Tom's help to get it right.

narfi
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Re: I need Propeller and or engine help

Post by narfi » Mon Aug 03, 2020 3:57 pm

The guy at the prop shop was pretty nice on the phone, he sold me a Michigan 13.75x13 because they didn't have any 12.x in stock.
He said he could exchange it once I had tested it for exact sizing.
He will deliver it to the Air Taxi on Wednesday, so I wont have to pay an expediter to pick it up for me.

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OrangeQuest
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Re: I need Propeller and or engine help

Post by OrangeQuest » Mon Aug 03, 2020 4:11 pm

narfi wrote:
Mon Aug 03, 2020 3:57 pm
He will deliver it to the Air Taxi on Wednesday, so I wont have to pay an expediter to pick it up for me.
:doh: :doh:
Strange language you guys use in Alaska. :lol:
Is that like AIR grub hub?
"that it isn't just an ordinary sort of boat. Sometimes it's a Boat, and sometimes it's more of an Accident. It all depends." "Depends on what?" "On whether I'm on the top of it or underneath it."
A. A. Milne

narfi
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Re: I need Propeller and or engine help

Post by narfi » Mon Aug 03, 2020 4:34 pm

OrangeQuest wrote:
Mon Aug 03, 2020 4:11 pm

:doh: :doh:
Strange language you guys use in Alaska. :lol:
Is that like AIR grub hub?
I live 150 miles from the closest road system.
I do not live on an island.
The only way to get where I am is by flying in a small airplane.
I live in a small village of some 200 residents that is made up of 2 parallel gravel runways, with gravel driveways shooting off from them. no stores, no restaurants, nothing like that here. (there is a food truck in the summer during tourist season)
My wife cuts her own hair, we don't eat out, my son hadn't had McDonalds till he was 5 or 6, etc... It is a different way of life.

So, if I want something, I order it from Amazon, or order it from a shop in Anchorage that is willing to deliver it to the airport where an air service (air taxi) will fly it to where I live on their next flight this direction, OR I pay someone (an expediter) to do my shopping and deliver it to the air taxi for me.
There is a post office here, so Amazon free shipping is better than the $1 per lb for freight and groceries most people here pay (I get an employee discount)

This pandemic has actually made life easier for me, as shops are much more used to phone orders and delivery now for the general public, and so getting deliveries is a lot easier for me now than it was say 6 months ago.

Does that make sense?

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cape man
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Re: I need Propeller and or engine help

Post by cape man » Mon Aug 03, 2020 4:47 pm

That 13 will tell volumes. Good luck.
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

narfi
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Re: I need Propeller and or engine help

Post by narfi » Mon Aug 03, 2020 5:02 pm

cape man wrote:
Mon Aug 03, 2020 4:47 pm
That 13 will tell volumes. Good luck.
an oldtimer here had an old nasty 14x13 (also black max) he had replaced, Ill grind the jagged bits off of it and give it a test this afternoon as well. (sun is out and family wants to go find a beach)

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