Hello
At my 2011 works a Mercury 60 EFI bigfoot (2011) with a PROP 14/11.
With full ballast tank it gets max 4700rpm and max 12kn (2 people and complete rig mounted).
Can I improove speed and economics with an adequate prop? I guess that it makes no sense to have a 60hp and cannot get out the HP that will arrive over 5000rpm.
Thanks for telling me your experiences with the same boat and Mercury 60HP EFI bigfoot.
Your motor is way over propped for your boat. I looked up the Mercury Bigfoot 60 specs. Max RPMs is 6000 / 1.83 (gear ratio) = 3279 max prop RPMs.
Our Suzuki DF90 prop is nearly maxed out for our boat with mast down and empty; Max RPMs is 6300 / 12.59 (gear ratio) = 2432 max prop RPMs. Loaded with mast up it could use even less prop which is currently a Solas Amita 4 blade 13.75 x 14ish (repitched down from 15). In theory, if you add 1" pitch the three blade equivalent would be 13.75 x 15.
The 60 is trying to turn a 4% larger area prop 35% faster at max rpm. For our 90 to be able to turn your prop with your gear ratio that fast we would need to remove roughly 3.5+ pitch from our 3 blade equivalent; 3279-2432 = 847 / 250 RPM per inch pitch = 3.4 pitch + something to compensate larger area prop. So your prop on our 90 with your gear ratio would be close match on our 26X.
The M is more of a displacement haul and really benefits from a 4 blade tractor type prop, like we installed on our Honda 50 (per Erik).
You should use a smaller diameter, smaller pitch, 4 blade prop. The smallest Solas Amita 4 blade I found for you motor is a 13.25 x 13 (1413-133-13). You could have a prop guy remove up to 2” pitch. Likely still too much prop.
Keep in mind our Honda BF50 (2001) used a Solas Amita 4 blade 11.8 x 9 with a Max 6000 RPMs / 2.09 (gear ratio) = 2871 max prop RPMs. Your motor only has 16% more HP would actually be a close match with this prop using your “lower” ratio higher prop speed.
All math is approximate with engine specs / gear ratios and props (which apparently are an art form). Just my thoughts from our recent experimentation.
Thank you for posting. I get 14 knots with my 50HP Mercury.
kurz wrote:Hello
At my 2011 works a Mercury 60 EFI bigfoot (2011) with a PROP 14/11.
With full ballast tank it gets max 4700rpm and max 12kn (2 people and complete rig mounted).
Can I improove speed and economics with an adequate prop? I guess that it makes no sense to have a 60hp and cannot get out the HP that will arrive over 5000rpm.
Thanks for telling me your experiences with the same boat and Mercury 60HP EFI bigfoot.
Greetings - kurz
Last edited by dlandersson on Mon Jul 16, 2012 2:47 pm, edited 1 time in total.
I have an 05 M and an 05 Mercury 50 HP EFI BF I run a 14x10.. My numbers are better than whats being posted and I haven't a clue why...
All Things being equal? This is entirely Mathematical.. Its been years, since I have run my boat WOT.. so I have Zero recent data..
What am I missing??
Divecoz wrote:I have an 05 M and an 05 Mercury 50 HP EFI BF I run a 14x10.. My numbers are better than whats being posted and I haven't a clue why...
All Things being equal? This is entirely Mathematical.. Its been years, since I have run my boat WOT.. so I have Zero recent data..
What am I missing??
My guess would be the 4 kids and 2000 lbs. of gear in a boat that's being used as a camper?
kurz wrote:With full ballast tank it gets max 4700rpm and max 12kn (2 people and complete rig mounted).
What does it do with the ballast tank empty? My picks up a lot of speed when the tank is empty, or while it's emptying if I drain it by running at speed. With the smaller 3-blade prop on my BF50, I don't see a huge engine speed increase. A big prop like yours is probably a bit more sensitive to speed.
Having said all that, it sounds overpropped to me, but that's based on not much.
works a Mercury 60 EFI bigfoot (2011) with a PROP 14/11.
picks up a lot of speed when the tank is empty, or while it's emptying if I drain it by running at speed. With the smaller 3-blade prop on my BF50, I don't see a huge engine speed increase. A big prop like yours is probably a bit more sensitive to speed.
