www.iFourWinns.com

Dedicated to Current and Future Owners
It is currently Fri Mar 29, 2024 8:01 am

All times are UTC - 6 hours [ DST ]




Post new topic Reply to topic  [ 5 posts ] 
Author Message
 Post subject: Bimini Fuel Economy
PostPosted: Tue Oct 24, 2017 5:42 pm 
Offline
Clownfish
User avatar

Joined: Mon Sep 25, 2017 11:51 pm
Posts: 41
Location: Thumb of Michigan
Has anybody ever compared fuel economy at cruise with a Bimini up compared to rolled in it's cover? I've heard various opinions but wonder how much additional drag a bimini on edge would actually present.

Tim

_________________
1987 Sundowner 215
Mercruiser 230/V8 - Alpha One Gen 1
Previous Boat
1973 Starcraft 21' Chieftain 120 HP Mercruiser I/O
PADI Master Diver
IANTD Technical EANx Diver
Commercial Pilot
Flight Instructor


Top
 Profile  
 
 Post subject: Re: Bimini Fuel Economy
PostPosted: Tue Oct 24, 2017 9:51 pm 
Offline
email admin your custom rank

Joined: Sun May 20, 2012 4:31 pm
Posts: 873
Location: Minneapolis, MN
If you are talking about while the boat is on the water, your fuel economy will probably be less than 4 mpg. The difference in frontal area (aerodynamic drag) between an open bimini and a stowed bimini would be minimal. If you could accurately measure fuel economy difference it would probably be no more than a few hundredths of a mile per gallon. This would not be enough for me to leave the bimini stowed on a warm summer day. I would stick with personal comfort to determine whether to open the bimini and let it go at that. If you were to try to measure it, you would need a calibrated digital tach to get the same RPM and a fuel flow with digital readout connected to a GPS.

_________________
Surface Interval: A scuba diving term for that time between dives to relax and prepare for life's next great adventure.

Current boat: '02 FW 268 Vista
Previous boat: '95 FW 190 Horizon


Top
 Profile  
 
 Post subject: Re: Bimini Fuel Economy
PostPosted: Wed Oct 25, 2017 9:39 am 
Offline
email admin your custom rank

Joined: Sun Jul 22, 2012 5:10 pm
Posts: 2032
Location: West Palm Beach, FL
Surface Interval wrote:
If you are talking about while the boat is on the water, your fuel economy will probably be less than 4 mpg. The difference in frontal area (aerodynamic drag) between an open bimini and a stowed bimini would be minimal. If you could accurately measure fuel economy difference it would probably be no more than a few hundredths of a mile per gallon. This would not be enough for me to leave the bimini stowed on a warm summer day. I would stick with personal comfort to determine whether to open the bimini and let it go at that. If you were to try to measure it, you would need a calibrated digital tach to get the same RPM and a fuel flow with digital readout connected to a GPS.

That was my thoughts exactly...
Wild ass guess: 3.00 mpg with Bimini up / 3.02 mpg with Bimini Stowed.

_________________
Image
"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings


Top
 Profile  
 
 Post subject: Re: Bimini Fuel Economy
PostPosted: Wed Oct 25, 2017 12:30 pm 
Offline
Clownfish
User avatar

Joined: Mon Sep 25, 2017 11:51 pm
Posts: 41
Location: Thumb of Michigan
Your replies mostly go along with my thinking.... I'm not ambitious enough to go to all the trouble to nail it down to the last tenth of a mpg. As it is, a boat has many drag producing elements as it is that can sometimes be mitigated but not eliminated.

I realize that boating and fuel economy do not go hand in hand..... aircraft tend to use a lot of fuel per hour too, only they do a lot better in the speed department. I have a lot to learn about my Sundowner and plan to experiment with loading, trim and power settings to see what will give me a decent speed and reasonable economy. I'm not a kid who has to be at full throttle all the time.... rather, a prudent sailor who prefers to know his vessel and how to get decent performance from it. For that reason, I appreciate you sharing your knowledge and experience with me.

In the FWIW department, my last two trips this fall showed an interesting contrast in fuel consumption..... The first, a 35 mile trip on the St.Clair and Black Rivers by Port Huron, MI, consumed 11 gallons of fuel. Thirty of the miles were on plane running down and up the St. Clair while 5 were at no-wake speeds on the Black. The St.Clair was pretty smooth (except where the river begins at the foot of Lake Huron) but not glassy. The second trip of 24 miles was on Lake Huron, from Port Sanilac to Lexington and back. Waves were running 1 foot or so and I was on plane at 22-24 mph. Fuel consumed, 10.8 gallons...... Loading in both cases was almost identical. Wind and wave action were the main difference, but it surprised me that it would have that much of a effect. Like I said, I have lots to learn which is part of the fun.

_________________
1987 Sundowner 215
Mercruiser 230/V8 - Alpha One Gen 1
Previous Boat
1973 Starcraft 21' Chieftain 120 HP Mercruiser I/O
PADI Master Diver
IANTD Technical EANx Diver
Commercial Pilot
Flight Instructor


Top
 Profile  
 
 Post subject: Re: Bimini Fuel Economy
PostPosted: Wed Oct 25, 2017 2:19 pm 
Offline
email admin your custom rank

Joined: Sun Jul 22, 2012 5:10 pm
Posts: 2032
Location: West Palm Beach, FL
Oldav8tor wrote:
Your replies mostly go along with my thinking.... I'm not ambitious enough to go to all the trouble to nail it down to the last tenth of a mpg. As it is, a boat has many drag producing elements as it is that can sometimes be mitigated but not eliminated.

I realize that boating and fuel economy do not go hand in hand..... aircraft tend to use a lot of fuel per hour too, only they do a lot better in the speed department. I have a lot to learn about my Sundowner and plan to experiment with loading, trim and power settings to see what will give me a decent speed and reasonable economy. I'm not a kid who has to be at full throttle all the time.... rather, a prudent sailor who prefers to know his vessel and how to get decent performance from it. For that reason, I appreciate you sharing your knowledge and experience with me.

In the FWIW department, my last two trips this fall showed an interesting contrast in fuel consumption..... The first, a 35 mile trip on the St.Clair and Black Rivers by Port Huron, MI, consumed 11 gallons of fuel. Thirty of the miles were on plane running down and up the St. Clair while 5 were at no-wake speeds on the Black. The St.Clair was pretty smooth (except where the river begins at the foot of Lake Huron) but not glassy. The second trip of 24 miles was on Lake Huron, from Port Sanilac to Lexington and back. Waves were running 1 foot or so and I was on plane at 22-24 mph. Fuel consumed, 10.8 gallons...... Loading in both cases was almost identical. Wind and wave action were the main difference, but it surprised me that it would have that much of a effect. Like I said, I have lots to learn which is part of the fun.

I've done a number of trips over 80 miles each way in my H240. I get a little less than 3mpg (like 2.85 or 2.9) with a good load in the boat. My 5.7L is carbureted, so those with Fuel injection would see about 15% better than that.

The most important thing is to stay at an efficient "cruising speed" which for most is 3000-3500rpm. Next is to "trim up" for the least water drag. Without changing the throttle, you can change the trim for best GPS speed. Generally UP is more efficient, but if your bow starts to bounce up and down then your too high. Or if the rpm jumps up (prop aeration) then your too high. Every boat model is a little different, but your GPS can help fine the most efficient trim.

You could also try your Bimini Up vs Down experiment the same way...leaving the throttle the same on smooth water, see if you can see a GPS speed difference with the top up or down.

_________________
Image
"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 5 posts ] 

All times are UTC - 6 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group