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Old 30 March 2016, 16:51   #1
Country: USA
Length: 5m +
Join Date: Mar 2015
Posts: 14
Prop advise for F70 on Achilles SU18 inflatable

Hi all,

I'm replacing an old Honda 50 tiller with a Yamaha 70 on a Achilles SU18 inflatable and was looking for advice on diameter and pitch for props. Because we beach it several times a day and the floor is all sand and gravel, I was thinking SS would be better option compared to aluminum. The boat is generally used to haul 2-4 people and gear for 3-5 day camping trips in the arctic. I'm really looking for something that can jump right up on step and carry a load and don't really care much about top speed (we are often operating in shallow lagoons and getting on step quickly is very helpful; plus there is lots of ice up here so we are never really going very fast anyway)

Thanks much!

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Old 31 March 2016, 08:16   #2
Fstarocka's Avatar
Country: South Africa
Town: Cape Town
Length: 4m +
Engine: Mariner 60 3cyl 2str
Join Date: Jan 2016
Posts: 90
Not familiar, but look at the new mercury spitfire props, great holeshot - and hubs to convert to other brands iirc.. anyway - you prob want to go lower on pitch for the weight..

Look on the mercury mariner prop selection here -

Mercury Prop Selector/

You can choose a few options - play around and compare the results..

I punched in a quick check based on your hp (not sure what motor) but assumed the 4 stroke 70hp yamaha with a total weight (excl motor) of about 690kg (boat / gear / ppl) and got this:


Boat type: Rigid Inflatable
Usage: Overall good performance/0 ft
Engine Manufacturer:
Engine Type: Outboard
Engine Year: 2011
Number of Engines: One
Engine Family: 4 Cyl 4-Stroke
Engine: F70 4-stroke
Drive / Gear Case: Yamaha T50-T60 4-Stroke (High Thrust) 2.33 Ratio

Calculated Pitch: 17.33
Calculated Weight with engine(s): 1,783.35 lbs
Calculated Engine RPM: 5,800
Calculated Boat Speed: 38.41 mph

Prop suggestions:

Black Max® Mercalloy 3 13.25 17 RH 77344A45
SpitFire® Mercalloy 4 13 17 RH 8M8026590
Vengeance® Stainless 3 13.125 17 RH 854356A46
Vengeance® Stainless 3 13 18 RH 16988A46
Good luck!

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Old 31 March 2016, 08:28   #3
Fstarocka's Avatar
Country: South Africa
Town: Cape Town
Length: 4m +
Engine: Mariner 60 3cyl 2str
Join Date: Jan 2016
Posts: 90
also - I would strongly suggest you get a shear type hub - i believe the mercury ones are field replaceable - in case you hit something solid, with SS u can do alot of damage to trans - just check it out -

Carry a few spares with you.. considering your location id also opt to carry a spare prop too!
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Old 31 March 2016, 16:30   #4
Country: Australia
Town: Dalmeny
Make: zodiac
Length: 5m +
Engine: outboard
Join Date: May 2015
Posts: 405
I've got a solas stainless 13 3/4-13 on my yam f70 which pushes my zodiac 550 pro. It pushes my outfit along at the same speed as yamahas aloy 15 but allows me to reach 6100rpm where the 15 only reached 5400.

I've just come back from a trip where I was talking with a hire boat owner using twin f 70 yams, he showed me his hour meter which was over 6000 hrs. He claimed their second tour boat has clocked 10000 hrs also with twin f 70's all without any failures.

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Old 01 April 2016, 10:00   #5
Country: USA
Town: Oakland CA
Length: 3m +
Join Date: Feb 2005
Posts: 6,620
When I operate in shallow water, I switch out the SS prop for aluminum. Repair of a bent SS prop will run the cost of replacing an alloy prop.

If I'm planning on loading up with divers, I run an inch or two shorter than normal - gives enough grunt to get on plane when loaded at the expense of top end (which doesn't come into play all that much in the coastal Pacific anyway.)

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