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Gas Consumption

pete31

pete31

Regular Contributor
Gentlemen.
First off let me start by saying I know my boat is a pig on fuel ( 1989 Carver Santego 34.. with a pair of 454 Bluewaters) but I was wondering if anyone had some sort of an idea of what the fuel burn should be. I have done a major overhaul of the engines, but was wondering if the carbs might be getting a little old.?
I have tried looking for old boat tests done on the boat and have been unable to come up with anything, other than the original sales brochure .Lots of pretty pictures of beautiful people relaxing in the sun. I would love to know best cruise etc..any help would be much appreciated, by the way the boat tips the scales around 16,000 lbs, 4 blade props and wot on the motors is supposed to be around 4200..4400 rpms

Thanks Pete
 
Fuel burn for any engine in GPH is independent of weight, etc, but rather is directly related to EXTRACTED HP. What your boat does with the HP is another story.... Most gas engines do about 1 GPH per 10 HP extracted.
 
Big block Chevies like that usually burn about 12 to 16 gallons an hour (each) at cruising speed. Face it, boating ain't cheap!

Jeff
 
Mine kills at least a 30 pack each and every day I use it...............not sure how to keep that consumption down................
 
Keep in mind that GPH must be associated with distance traveled. In other words, GPH alone is not a good means of determining fuel economy unless you also know the distance that you travel in that HOUR.

What you want to concern yourself with, is Miles Per Gallon!



.
 
Sailed for many years.... annual cost of sails and rigging when amortized over life of sails, gets to look a whole lot like a bill for a seasons worth of gas for a small to moderate size powerboat and moderate useage. And yes.... many blowboaters are....cheap! no polite way to put it.
 
Thanks for the input..have to do a little more digging, try and find out what the best cruise speed is for the fuel being burnt
 
I would be more worried about RPM than cruise speed and fuel consumption. If you find the best speed for the best fuel consumption it may be too low of an RPM and will end the life of your engine. Lugging is bad. Cruising at 3000-3200 rpm will unload the engine.

If you cannot get around 4600 at wot, you have other problems to address first.

The amount of fuel you think you will be saving will be spent ten fold on a new engine.
 
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I'd invest in a Flo Scan unit to determine what fuel burn you're getting.

I had one on my old boat and it was a terrific tool for analyzing engine performance; when the 'known' usage rate dropped, I went searching for the reason.

A bit of math will give you that all important mpg, as Rick mentioned above. On mine, the best mpg was achieved just above the speed needed to maintain plane but, if I had a wide stretch of boring water to cross, I could throttle up to a slightly less economical speed to 'get it over with'. And on those days when I had a 'heavy hand', I could see how thirsty things could get and back way off!

Jeff
 
pete31 said:
..................... have to do a little more digging, try and find out what the best cruise speed is for the fuel being burned
Click to expand...

**As a general rule....... for most any planing type hull this speed will be in the range whereby the hull is fully up on step, and just a tad bit more.

As Chris suggests...... if the engine's RPM is too low during this hull attitude, you will over-burden it and you will shorten it's life.
Likewise, if the engine's RPM is too high for this hull attitude.




fastjeff said:
I'd invest in a Flo Scan unit to determine what fuel burn you're getting.
Yes!

A bit of math will give you that all important mpg, as Rick mentioned above.
On mine, the best mpg was achieved just above the speed needed to maintain plane
This is exactly what we want to do in order to reduce friction and gain fuel economy! (see ** above)
Click to expand...

 
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My suggestion is,

1. don't mention timing.
2. don't mention pistons

3. drive like you stole it and enjoy it.

If you cant afford the fuel either get a smaller boat or a better paying job
 
kimcrwbr1 said:
Put a timing light on the engines and find out the rpm for max spark advance then run your engines at that RPM will give you the best fuel economy.
Click to expand...

All due respect...... some OEM ignition advance curves will continue past the recommended cruise RPM.
In other words, the spark lead will continue into the 4k+ RPM range.
In many cases, the proper "cruise" RPM is no where near WOT RPM.


Our ignition advance has the last word in where the LPCP will be. We want to achieve the correct LPCP, yet not allow Ignition Induced Detonation to occur.
Detonation can/will be at it's worst potential in the 2K to 3K rpm range...... so by all means avoid sustained operation at this RPM.
I suggest that we get through this range as quickly as possible and into our Up-on-Step RPM range and lesson the burden on the engine.
 
Had a long talk with one of the product engineers @ an OEM marine engine MANUFACTURER, not marinizer, some years ago (early 1990s).. as best I remember @ WOT engine life measured in 10s of hours to low hundreds. @ 80% of WOT gets to 1000 hours. @ 70%... 2 to 3000 hrs, especially if "fresh" ( Yes Rick, I know! :) ) water cooled with a 160ish T'stat and regular oil changes and good oil.
 
thank you all for the words of wisdom..after going over my notes from last yr and doing a little more digging..looks like its about $100 per 20 miles..going by the bend over and grab your ankles pricing at the marina fuel pump..regardless of weather the boat is putting along at 1100 rpm..or lifting her skirt and doing 3000.rpm..and I have already checked the timing..( all good)..and that she will hit 4400 rpm with half the house packed into it, so I just need to find the sweet spot where I can lift the tabs a little and still maintain the same speed..wont be long before she is back in the water..
thanks again
 
Not sure if your marina will allow this--most don't--but you can buy a 'gas caddy' (rolling fuel tank) and refuel your boat with much cheaper local gas station fuel.

Jeff
 
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