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Old 24 June 2015, 04:21   #21
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Country: UK - England
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Boat name: Bombard, Y-162
Make: Aerotec 380, Y-Class
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Engine: Mercury Mariner 15hp
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I need to correct that! I found another post on here I made last year and the figure was 5700 I think not 5200. Also forgot the rubber floor (pretty heavy stuff) at + 7.5kg.

I read a load of stuff on prop pitch and all the calcs to go through last night and Mercury's own prop calculator comes up with the same 9x9.

From what I understand I could go to a 10 pitch to increase top speed but that would lower pick up and bring me down to 5500.

Or maybe an 8 pitch to help pick up but that would lower top speed and raise RPM to 5900.

I want to raise top speed and pick up though which sadly I guess is unattainable in the same prop and the standard 9x9 is the compromise option?

I wonder if a stainless prop would offer any gains in this situation or going to a 4 blade which I gather lowers RPM by 100 or so due to the increased drag, although I guess SS props with thinner blades have less drag...?

Anyone?

I'll stick some links I found in below as they might be handy to anyone reading this topic in the future.

Choosing The Correct Propeller For Your Outboard | eBay

Understanding your Boat Propeller

Prop Basics, how propellers work

Understanding Propeller Pitch | Boating Magazine

https://www.mercurymarine.com/en-gb/...tor/#/step-one
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Old 24 June 2015, 05:37   #22
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>>>From what I understand I could go to a 10 pitch to increase top speed but that would lower pick up and bring me down to 5500.


Now surely with a 10 (for example)... assuming your outfit/payload allows... you can either choose to allow it to still rev at 5700 with a higher speed... or keep to the same speed with lower revs???

If you are getting to 5700 on a 9 it seems a 10 may work for a better top end... only way to find out though is to spend and experiment!

My experience with other than Mercury own props has been poor... I sent a Solas one back as it ruined performance... different blade shape was obvious when held side by side... made a massive difference.

Stainless risk gearbox damage if you hit an object or rock as I understand it... which is why for sibbing in Scotland I'd not use one. Also I believe with stainless the pitch requirements change and it is very much trial and error so ideally you need to be able to borrow different props.
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Old 24 June 2015, 07:24   #23
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Yep, stainless is a fortune anyway, pretty pointless probably on a little old 15 I guess.

I need to borrow a 8 and 10 pitch to try back to back to see the real world difference.
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Old 24 June 2015, 07:47   #24
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Just a though. I've always had great service from Steel developments. How about seeing if they has a refurb in 8 or 10 pitch and asking if they would agree to take it back (assuming undamaged) for a handling fee if the pitch was found unsuitable??
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Old 24 June 2015, 14:58   #25
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Thanks for bringing this post back. You're right in that it has a lot of useful information and I had never seen it before.

I've been having a similar question as yours. I run a 20hp on a large boat with a little heavier load for our own reasons. I didn't have a tach so I don't know where we were at for WOT but we were able to do 14-16 mph with the standard Mercury 9.25x10 prop. Just by the sound of the engine I believe we have a lot of room to get up to the 5800-6100 range.

I got a tachometer which I just installed. Ran through a lot of various calcs and read as much as I could and settled on a 9 pitch prop. Bought a cheap aluminum Solas 9.25x9 prop to try out. I can see a big enough difference between the Mercury Black Max and the Solas that if it gives a decent improvement, I will buy a Mercury and keep the Solas as a backup.

Hoping to take it out this weekend and get some readings fully loaded.
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