need to improve fuel economy

[enjoy2]

I have a great 370 sedan bridge ( 1993 ) with 454's with 980 hours . The engins run well amd have been maintained Professionaly by me( 10 years) and the prior owner . I am getting ready to retire and dosee not my ability to cover the fule cost when burning 45 gph at 16-18 knots at 35-36 hundred RPM's . Am out of the norm ? Do I consider rebuilding or is this it . If I can re-power or modify and get to 30 gph I would seriouly consider or I will be downsizing reluctantly . Any advise to keep me in this boat will be well appericated . Enjoy 2

 

[northern]

We have the same engines. Ours have 1,750 hours and work well. Local Mercruiser deal feels I am half way through the engines before they need work. No loose of power since we go the boat at 650 hours. We cruise at 6 knots and 1200 to 1400 RPM. At that speed we burn 1 US gallon per knot. If we turn one engine off and go 5 knots we burn about 3/4 gallons per knot, but it is a pain to steer. We do go fast when we have to, but 90% of the time we go slow. If you retire you have more time to get places. We used to go fast but now we have time. I thought of down sizing but we would miss the room. If you repower with 135 HP deisel you might get better fuel burn but I think the boat would have little resale value. We allow for $10,000 a year for fuel. This year we night use $6,000. At the price to repower we can burn a lot of fuel.
Keep us posted on what you do. There are lots of us in your position.

 

[Billfletcher]

You should consider more time on the hook. My anchor has become my best friend on our boat. This weekend I did a slow cruise to a sheltered cove 3 miles away and hung there all day. We then motored a couple miles and listened to a concert in a nearby park until 10 pm on the anchor, and watched the fireworks from a barge 500 ft away. It was great. Fuel costs minimal.

 

[Theresamarie11]

I have a great 370 sedan bridge ( 1993 ) with 454's with 980 hours . The engins run well amd have been maintained well by me( 10 years) and the prior owner . I am getting ready to retire and can not my ability to cover the fule cost when burning 45 gph at 16-18 knots at 35-36 hundred RPM's Am out of the norm and need to rebuild or is this it . If I can re-power or modify ad get to 30 gph I would serioulyh consider or I will be downsizing reluctantly . Any advise to keep me in this boat will be well appericated . Enjoy 2

I don't know what the cost of repower is, but have you looked at it's resale value versus replacement cost (taking benefit of sale of your current boat) of similar already powered with diesels? We have some friends on Champlain with a big sedan cruiser with twin 454's and he can't sell if for just the fuel cost reason. There are lots of boats for sale and you may find the right buyer who wants to go fast and you can settle into something more economical. If fuel costs keep on going up, it might get harder over time to trade it in. But then the cost of fuel on Champlain is close to $5/gallon (still).

 

[ardeprint]

Have you considered a set of used diesel engines? To me It might not be worth the expence, but to you perhaps an option.

 

[moparlvr4406]

very long oars...
but your food bill will raise considerably

 

[rcknecht]

Unless you re-power with diesels you won't see a substantial increase in fuel economy... Your boat is big and heavy... If you go a displacement speed you can get much improved economy. Your maximum displacement speed is a factor of the our length at your water line. Typically, a boat of your size the maximum displacement speed is about 9 to 10 miles an hour...

 

[MasterFab]

Everyone here has the issue pretty well surrounded. I can tell you that a slight improvement in your planing fuel economy is possible, as I have accomplished a considerable increase in my own fuel economy as compared to a factory 340, but I was restoring my vessel to begin with. I revised the trim tab geometry and size, profiled the rudders and struts, smoothed and fared the vessel's bottom, updated the props to CNC 4 blades from ACME, and reduced weight in the engine room to provide for a more level and efficient ride.

In your case, with a comparatively heavy boat, all the above modifications might improve your economy 10-15%, but a lot would depend on the current condition of your bottom, props, engines, etc. If your bottom is really rough and the props are bent, you could see a substantial increase. Otherwise, it would be more subtle. As Rod intimated, traveling at or below your hull speed is the way to go for best economy. Once on plane, fuel usage increases exponentially.

Your goal of a 33% reduction in fuel usage, at planing speeds, is not economically feasible. It would cost so much more to get to that level of efficiency (only diesels will do it) that it makes no economic sense. I have posted some of my thoughts concerning economy and efficiency on my blog, if you want to review it, but again, none of these things will yield a 33% increase in economy.

 

[northern]

We are retired. We go north each summer and into Washington in the fall. We burn twice what a new deisel boat does at slow speed. Old used deisel boats we have talked to seem to burn 2/3 what we do to go the same distance but they travel at 10+ knots. I can fix gas motors but have no idea how to fix a deisel engine. One person with a 60 foot deisel tug converted to a cruiser I met told me his tool box was his cell phone. Until we retired fuel was the low cost on our boat costs. We now spend more on fuel than moorage. That I think is a good thing.

 

[rcknecht]

Your boat is not designed as a displacement hull. You have a planning hull. Even if you had diesels they would still get better fuel economy. I hope that fuel prices will come down soon and our economy will pick up steam. But as the fellow from beautiful San Diego said, "your anchor is your best friend"

 

[joe and ali]

We run our boat under 2000 rpm at 2000 rpm, we run 10.2 mph at max, we run at 9mph most the time. Last year we did 550 miles for the summer and used about 480 ga. of gas no tide, not much current up here.

 

[Gofirstclass]

The concept of dropping your fuel burn from 45gph to 30 gph means a 33% decrease in fuel consumption. There's no way to get to that 30gph number with your boat without spending about $100,000 to drop in a new pair of diesels, and even then you might not get to 30gph.

The problem is, like others have said, is that you're spending too much time running on plane. Yeah, you have a planing hull and it will easily run on plane, but it's VERY expensive as you're seeing. I used to run my 330 Dancer on plane all the time because I could get 1mpg on plane or at hull speed. I figured if I was going to get the same mpg at both speeds I'd run fast and spend more time at my destination.

Now I'm getting used to cruising at "cocktail speed". In my boat that's just under 1000 rpm's and right at 9.5kts-10kts.

The forumula for finding the hull speed is: the square root of 1.34 * LWL (LWL = length of the boat at the water line)

Do your calculation using your LWL and you will know your boat's best hull speed. Learn to love that speed and you'll be spending a lot less on fuel without having any repowering costs.

 

[HUMPH]

Unless you re-power with diesels you won't see a substantial increase in fuel economy... Your boat is big and heavy... If you go a displacement speed you can get much improved economy. Your maximum displacement speed is a factor of the our length at your water line. Typically, a boat of your size the maximum displacement speed is about 9 to 10 miles an hour...

I burn less than 30 GPH at 20 knots.

 

[Alex F]

......The forumula for finding the hull speed is: the square root of 1.34 * LWL (LWL = length of the boat at the water line).....

Based on my findings, the formula is:

The hull speed formula for displacement monohulls is 1.34 x the square root of the waterline length. When planing, a monohull will exceed it's hull speed.

My question is, does the speed measured in KTS or MPH in this formula?

 

[stephane]

Diesel is the only way to get fuel economy in a boat. I convert mine 3 years ago and never look back I will keep the boat many years and love it as it cost almost sweet noting to run now. I save 6-7 k of gaz per years and my boat will is keep value. Also I prefers to invest my money in good engine than burning it in fuel....

 

[Bermuda Shorts]

One simple fix is to make sure your back flame arrester is clean, When these are dirty and clogged your air mix will be off and your performance will suffer.

 

[Four Suns]

Angle your antennas back on the hardtop to make it more aerodynamic.

 

[enjoy2]

I appericate all the advise , which suggests go slow and Enjoy the ride or Hook . I just want to make sure my burn is not out of the norm and I have the opportunty to improve it . A diesel conversion is not a option , we would be better off in a different boat , which I have been eyeing the PDQ 41 ( 12 GPH at 17Knots ). Anyway , if the 45 GPH is not out of the norm , than for now I will slow it down to Hull speed . Thanks again to all who responded .