I need Propeller and or engine help

Power Boats only. Please include the boat type in your question.
narfi
* Bateau Builder *
* Bateau Builder *
Posts: 1868
Joined: Tue Jun 07, 2016 6:55 pm
Location: Bush Alaska
Location: Bush Alaska

I need Propeller and or engine help

Post by narfi » Sun Aug 02, 2020 1:08 pm

Fs17
New Mercury 60 command thrust

Mercury Blackmax 3 Blade Prop Propeller 12-3/4 X 21
(Cant remember why I picked that prop buy pretty sure I used an online calculator)

Max rpm with 10 gallons and 600lbs of people/gear is 3700rpm.

I thought i has the cable rigged wrong when max was 3500, but its at full travel now and only getting 3700.

I will check my rigging again but suspect I have the wrong prop.

Any thoughts or suggestions?



User avatar
cape man
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 6810
Joined: Sun Jan 20, 2008 12:02 pm
Location: Lithia, Florida

Re: I need Propeller and or engine help

Post by cape man » Sun Aug 02, 2020 3:20 pm

Bet you need a 14 or 15, not a 21.
The world always seems brighter when you've just made something that wasn't there before - Neil Gaiman

wadestep
* Bateau Builder *
* Bateau Builder *
Posts: 1406
Joined: Fri May 09, 2008 9:40 am
Location: SW Florida

Re: I need Propeller and or engine help

Post by wadestep » Sun Aug 02, 2020 4:26 pm

agree with Cape Man - a 21 pitch is probably WAAY too much prop. Not sure on your recommended top HP, but if it could get top RPM you'd be doing about 45MPH!
3 sizes smaller around 14-15 is likely to be about right.
wade
Completed : OB19, CC14, GV10.

Fuzz
* Bateau Builder - Expert *
* Bateau Builder - Expert *
Posts: 6825
Joined: Tue Aug 02, 2011 4:23 am
Location: Kasilof, Alaska

Re: I need Propeller and or engine help

Post by Fuzz » Sun Aug 02, 2020 4:39 pm

My dory has a Merc 50 on it. So a little heavier and a little less power. I am running a three blade 13 pitch. So that tells me that the guys guess of 14-15 has to be darn close. I would not keep on running as is. You are way overloading a new engine at break in time.

Rover1
Frequent Poster
Frequent Poster
Posts: 105
Joined: Sun May 14, 2017 6:57 pm
Location: Boston, MA

Re: I need Propeller and or engine help

Post by Rover1 » Sun Aug 02, 2020 8:12 pm

Narfi
I think the others are correct.
Start with the 14 or 15. My FS17 had a 50HP and the 12 pitch was a bit small. RPMs a bit high.
Rule of thumb Is 500RPM for each inch of prop pitch. Be careful of thumbs though.
Rover1

TomW1
Very Active Poster
Very Active Poster
Posts: 3232
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: I need Propeller and or engine help

Post by TomW1 » Sun Aug 02, 2020 8:43 pm

Narfi if you will give me till tomorrow morning I will run the numbers through my prop calcs. Need the weight of the boat, did you build the FS17 heavy or can I use the weight from the plans. That is should I use 315 or something higher. The only 60 Merc I could find was the EFI in there online information. It weighs 247lbs could you confirm the weight of your motor. Fuel size of fuel tank. Do you have remote control steering, 1/2 batteries, any hydraulics. I would guess we will be down at a 13 pitch by the time we are through. If your motor is like the 60 EFI we need to get you above 5500 rpm's at full throttle to keep the motor from wearing out pre-maturely, its top speed operating range is 5500-6000. Your motors Op range will be in the manual or under the cowl.

Look forward to hearing from you,

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

narfi
* Bateau Builder *
* Bateau Builder *
Posts: 1868
Joined: Tue Jun 07, 2016 6:55 pm
Location: Bush Alaska
Location: Bush Alaska

Re: I need Propeller and or engine help

Post by narfi » Sun Aug 02, 2020 9:11 pm

Built a little heavy. I estimate the moter around 250lbs. 19 gallon tank, 1 battery. Remote steering.

TomW1
Very Active Poster
Very Active Poster
Posts: 3232
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: I need Propeller and or engine help

Post by TomW1 » Sun Aug 02, 2020 10:19 pm

Narfi the folks that werIe going to stop by did not so I finished running your numbers. I found the numbers for your motor the big difference is it has a 2.33 final drive and gains about 8 lbs in weight. The 2.33 lets it drive a larger prop than I first estimated so here is what I recommend for you. Stay with the Black Max in the 12 3/4 but in a 16 pitch. This should put you in the 5500-6000 rpm range at wide open throttle, you of course will never use that much if ever, but that is how a prop is set up for optimum engine life. These calculations are only based on perfect conditions, weather, temp and other things come into real life and the numbers you gave me, if top rpm's are much over 6000 go up an 1" if under 5500 go down an 1". When I say much over 6000 I mean that you are hitting the over rev cut out all the time, a couple 100 won't do any harm since you won't be running there and can adjust to keep it below 6000.

If you would like to have me prop your boat for a SS prop let me know. They are more efficient and you would probably go up a pitch or so.

Good luck You will have a top speed in the upper 30's.

TomT
Last edited by TomW1 on Sun Aug 02, 2020 11:02 pm, edited 1 time in total.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

narfi
* Bateau Builder *
* Bateau Builder *
Posts: 1868
Joined: Tue Jun 07, 2016 6:55 pm
Location: Bush Alaska
Location: Bush Alaska

Re: I need Propeller and or engine help

Post by narfi » Sun Aug 02, 2020 10:48 pm

TomW1 wrote:
Sun Aug 02, 2020 10:19 pm
Narfi the folks that werIe going to stop by did not so I finished running your numbers. I found the numbers for your motor the big difference is it has a 2.33 final drive and gains about 8 lbs in weight. The 2.33 lets it drive a larger prop than I first estimated so here is what I recommend for you. Stay with the Black Max in the 12 3/4 but in a 16 pitch. This should put you in the 5500-6000 rpm range at wide open throttle, you of course will never use that much if ever, but that is how a prop is set up for optimum engine life.

If you would like to have me prop your boat for a SS prop let me know. They are more efficient and you would probably go up a pitch or so.

Good luck

Tom
Appreciate it. And yes I would like to know my options for when I call tomorow.

Thanks!

What stores normally stock propellers? I got this one off of Amazon but will be looking for one in anchorage tomorow.

TomW1
Very Active Poster
Very Active Poster
Posts: 3232
Joined: Sun Apr 19, 2015 10:57 pm
Location: Bryson City, NC

Re: I need Propeller and or engine help

Post by TomW1 » Sun Aug 02, 2020 11:56 pm

Narfi there is not much difference in diameter whether a SS is 12 1/4 or 12 3/4 that is equal to about 1/2 a pitch, but I would go up 2 inches in pitch if you go SS. An 18 pitch vs the 16 pitch. If I were you I would get the aluminum and get it dialed in and then get an SS as the main prop with the aluminum as the back up.

I found this store which handles PowerTech Props in Anchorage they will probably stock others.
Alaska Prop Shop
10201 Elmore Rd
Anchorage, AK 99507

907-764-1012

Found this on the PT site. These are the props that I recommend and most of the guys use down here.

You can also go to the Wholesale Marine website, they ship to AK.
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

Post Reply

Who is online

Users browsing this forum: No registered users and 3 guests