Fuel Consumption

[JCD]

Hello all,

I have a 1984 Bayliner 3270 Yacht with twin inboard 165HP crusaders. I have her rigged for offshore tuna and large species like shark etc. Her maintenance schedule is immaculate and the motors purr like kittens. The hull is semi-displacement and she has trim tabs.

I know that she should operate somewhere between 11 and 15 mph in order for her to be "fuel efficient". If I wanted to just cruise around the bay at 6 mph in displacement mode without doing 15mph would I use up more fuel as compared to running her at her semi-displacement rpm? I never really took the time to measure these things because the tuna trips "paid" for these excursions and her full maintenance, but, there won't be any trips this year since the team broke up. I still want to use her. I think I get 6-8gph at 12mph, but have seen it closer to 1.2mpg when the tanks (270gallons) are full. I fill them to satisfy the 1/3, 2/3 rule but if I stay inshore I can probably take half the weight off.

Is there any simple way to measure it? It would be nice to just slow it down for a while and maybe watch the ladies sunning on the beach in Coney Island instead of a 100 mile offshore trip to the canyons for Tuna. Spring commissioning is almost here already. I hate those 2 weeks.

Any direction is appreciated.

J

[yipster]

Originally Posted by JCD

If I wanted to just cruise around the bay at 6 mph in displacement mode without doing 15mph would I use up more fuel as compared to running her at her semi-displacement rpm?

no no, you'll consume (a lot) less that way, you might be tempted to speed up a bit doing distances tho
very nice old boat, keep her up but do know boats are for idiots

[masalai]

Getting good Yipster. Big smilies & winking too. Trivia brownies if I can & thanks for the feedback. Like your model/graphic in email.

[charmc]

Originally Posted by JCD

I know that she should operate somewhere between 11 and 15 mph in order for her to be "fuel efficient". If I wanted to just cruise around the bay at 6 mph in displacement mode without doing 15mph would I use up more fuel as compared to running her at her semi-displacement rpm?
Any direction is appreciated.

This fuel consumption table is for a larger boat, but the principle is the same. http://www.boattest.com/boats/1004/test_results.aspx At 6 mph you will use only 20 -25% of the fuel you use at planing cruise speeds. Plus you get to see more of the ladies in the tiny swim suits! Not a bad way to spend an afternoon.

[pasty63]

I have an 86 3270 with the 110 Diesels. I find the hull heavier on displacement than semi, so pushing it faster seems to just use more fuel. Both my nautical miles per gallon, and my gallons per hour are better if I run about 8.5 kts. It would be interesting to know your nautical miles per gallon once you were on plane - I have only been able to push my boat to about 12 kts (current static), so I don't think I've ever achieved such a thing.

Thanks -.b

[JCD]

Hawdy,

CharmC, I'm not sure that the chart is indicative of my gph use. The crusaders are petrol and at 165HP it is a big difference. But thanks. How did you arrive at 25% less for 6mph?

Pasty63, these are beautiful yachts aren't they? I love mine and like Yipster pointed out...I'm her idiot. Anyway, here is the deal from what I remember, but never measured. Duh.

Full tanks, 270g , it took a lot longer to get out of the hump, but once I was out and on plane, I would get about 12 to 13 mph at 8 to 10gph, for about 1.3mpg.

Coming off the canyons with 800 to 1000# of Tuna, and approximately 90g less, I would return to port barely planing at 10mph, burning approximately the same. The plates had to be fully down!

If we had a bad weekend and I came back with 200 to 400# of Tuna, we would return by following the length of the canyon in semi-displacement hoping to hit a school with 18 rods set and 45 hooks in the water, burning an addittional 40 to 60g, for about 1.4mpg.

If we had an excellent weather week but a bad fish week, we stayed a lot longer and left with approximately 100g in the tanks, planed quickly to about 16mph when the tanks were almost empty and saw 18mph on surf. This was tough to judge for gph use because we motored on and off and drifted to fly kites to leeward, so the long hours never gave me a good estimate when I returned and filled her up. Those trips were few but they were a total financial loss. All of the above were based on engine hours.

It sounds like I may have to get an in-line fuel meter and do some rpm charts made up this summer. Thats going to be another boat buck.

Your figure sounds about right, 12knots=13.8mph, but, at what rpm are the hinos operating and what is your prop pitch? What is your gph and mpg?

Oh yes, no matter how well the trip paid, I always cried at the fuel dock while filling her up and when doing her full tune-up every 100 hours. Remajoring the motors every year was tear city.

Thanks
J

[pasty63]

Originally Posted by JCD

Your figure sounds about right, 12knots=13.8mph, but, at what rpm are the hinos operating and what is your prop pitch? What is your gph and mpg?

At 12 kts the Hino's are running 2800rpm and burning 10gph. At 2600 rpm it does about 11 kts and uses 6.5 gph. At 2200 rpm it does 8.5 kts and uses 4 gph. The props are 17 x 15 4 blade Michigans. Between 8 and 12 kts we run from 2 mpg down to about 1 at 12 kts - give or take.

I have our 3270 all apart right now - leaky fuel tank. So the engines and tanks are out right now, and I'm getting ready to do some stringer and transom work in addition to replacing the tanks. The engines will get some paint and new gaskets. Even with all the work - I still love it like an idiot.

[JCD]

Originally Posted by pasty63

At 12 kts the Hino's are running 2800rpm and burning 10gph. At 2600 rpm it does about 11 kts and uses 6.5 gph. At 2200 rpm it does 8.5 kts and uses 4 gph. The props are 17 x 15 4 blade Michigans. Between 8 and 12 kts we run from 2 mpg down to about 1 at 12 kts - give or take.

I have our 3270 all apart right now - leaky fuel tank. So the engines and tanks are out right now, and I'm getting ready to do some stringer and transom work in addition to replacing the tanks. The engines will get some paint and new gaskets. Even with all the work - I still love it like an idiot.

Oh yes...

That is pretty good usage. My rpm's is higher to top out the props. I think it's 3600, but if needed I can open up the throttle to 4200. Were both idiots. So what.

What are you doing to the transom? Are you replacing the tanks or sheathing them? How many hours on the hinos?

J

[pasty63]

Originally Posted by JCD

That is pretty good usage. My rpm's is higher to top out the props. I think it's 3600, but if needed I can open up the throttle to 4200. Were both idiots. So what.

What are you doing to the transom? Are you replacing the tanks or sheathing them? How many hours on the hinos?

We only have about 750 hrs on the Hinos and they are working great. They top out at 3000rpm, but their torque peak is early and flat

There are some spots in the transom that go "thud", and a fair amount of moisture in some others. I'm going to open them up with a hole saw and leave a dehumidifier in the engine room for a couple of months and see how it goes. Hopefully, I can just cut out the bad spots and glass in some new pieces instead of replacing the whole section. The stringers are very damp - same thing there - hoping that venting and drying will just give me a few spots to fix.

I am replacing both tanks and re-installing them correctly - rather than how the factory did it. Bayliner just slapped the tanks flat on chopper glassed plywood sections. Without proper venting between the surfaces, the tanks sat on the saturated plywood and developed corrosion. The port tank is still holding fuel - the stbd was losing about a pint a week in the bilge. Slow - but it wouldn't have gotten better on it's own. I've already rebuilt the seatboxes on the bridge and replaced the cockpit cabinet (with white seaboard), so I suppose after I fix up the stringers, transom and fuel tank bunks I'll need to redo the engine room bulkhead and (eventually, I hope) the flybridge deck. The only thing standing between great boat status and legendary boat status for the 3270 in my mind, is about $100 in 3M 5200 and shop floor labor at the Bayliner plant. They never sealed a thread or plugged a hole in the glass when they put all the amenities on the hull/decks.

Oh well - I guess it's up to me to put it together correctly now

[TollyWally]

For what it's worth I used the following technique to pull moisture out of a foam core once. I hooked up a shop vac hose to a plywood plenum, screwed the plywood over a holesaw cut hole in the inner glass layer. Then I let the shop vac run for a couple days. It seemed to pull the moisture out. I don't know exactly how well it worked but it sounded better and felt dry after the vac treatment. I then glassed back over the area. I didn't have the luxury of sufficient time to wait. My .02