Fuel burn 45’ vs 53’

[Hookedup2407]

Fuel burn 45’ vs 53’

Feel funny asking such a question. But i have an opportunity to purchase either a 53’ or a 45’ both are early 70s models in excellent shape for their vintage. The 53’ has original 12v71N 3yrs since MOH and the 45’ has 6v92TA (installed new in 2002) allegedly 800hrs since last major in 2013. I run a charter business so fuel burn will be a major deciding factor as well as overhaul costs.. Can anyone give me fuel burn stats trolling at 8kts (@800rpm) and running (at @1800) assuming they are both propped correctly and bottoms are both clean.. 53’ with 12v71N vs 45’ with 6V92TA (550hp) Thanks again

 

[Captain Ralph]

Re: Fuel burn 45’ vs 53’

Hull speed per model (economy & slow) is one thing.
Forgiveness and easier maintenance is another.
If you are not into high performance (10% maybe extra). always go for the 71s.

 

[Cricket]

Re: Fuel burn 45’ vs 53’

You will be able to fish a lot more days when it's rough on the 53', 53' is a really comfortable boat in all aspects and the cockpit on the 53' is much bigger. 12v71N's are very bulletproof engines, especially compared to the 6v92TA's, couldn't image having 6v92TA's in a charter boat. My guess is fuel burn is probably similar but others will have better insight.

 

[Briankinley2004]

Re: Fuel burn 45’ vs 53’

My 55 with 12-71 TI’s got 0.6 NMPG at hull speed (8-9 knots) I didn’t run them up often but I believe 50-60 GPH was the burn at 1800 rpm and I was lucky to get 18 knots if all conditions w ere perfect. I definitely would go 71’s over 6-92. I hear some parts for the 6-92’s are getting hard to find

 

[rsmith]

Re: Fuel burn 45’ vs 53’

My 50 with 12/71n’s burns 42 gph @ 2100rpm 19kts depending on fuel load. Trolling speed 850 is 10gph 9 kts.i run those 2 speeds nothing in between because the boat just runs better there more stable and the engines just sound happy there. I fished NE canyons for years with my 50 and ran several 46c’s with 8/ti’s pretty much the same hull as the 45 average day was 4:30am to 6 pm with a 4-1/2 hour run each way offshore at 2100. Fuel burn on my 50 averaged 435 gallons where the 46 was 365. Believe it or not those numbers were almost to the gallon trip to trip.

 

[Hookedup2407]

Re: Fuel burn 45’ vs 53’

My 50 with 12/71n’s burns 42 gph @ 2100rpm 19kts depending on fuel load. Trolling speed 850 is 10gph 9 kts.i run those 2 speeds nothing in between because the boat just runs better there more stable and the engines just sound happy there. I fished NE canyons for years with my 50 and ran several 46c’s with 8/ti’s pretty much the same hull as the 45 average day was 4:30am to 6 pm with a 4-1/2 hour run each way offshore at 2100. Fuel burn on my 50 averaged 435 gallons where the 46 was 365. Believe it or not those numbers were almost to the gallon trip to trip.

Thanks for that

 

[Hookedup2407]

Re: Fuel burn 45’ vs 53’

My 55 with 12-71 TI’s got 0.6 NMPG at hull speed (8-9 knots) I didn’t run them up often but I believe 50-60 GPH was the burn at 1800 rpm and I was lucky to get 18 knots if all conditions w ere perfect. I definitely would go 71’s over 6-92. I hear some parts for the 6-92’s are getting hard to find

92s aren’t my engine of choice… but it is nice to have the extra ponies when needed.. my concern is overhaul costs with the 12v71 vs 6v92s.. Overall cost of ownership seems more feasible with a 45 vs a 53. I know i prefer a 71 I’ve a 92 any day. But w 24 holes and 24 injectors has me leery..

 

[rsmith]

Re: Fuel burn 45’ vs 53’

92s aren’t my engine of choice… but it is nice to have the extra ponies when needed.. my concern is overhaul costs with the 12v71 vs 6v92s.. Overall cost of ownership seems more feasible with a 45 vs a 53. I know i prefer a 71 I’ve a 92 any day. But w 24 holes and 24 injectors has me leery..

I’ll take the 24 holes over turbo and intercooler problems.

 

[Fanfare]

Re: Fuel burn 45’ vs 53’

I now have about 30 years experience with 550 hp 6V-92TA Detroit repowers. They have been almost flawless, far better than my 8V-71Ns were (including the Allison transmissions). They don't even leak oil!

I am aware of the overheat problem but have redundant temperature and flow alarms, change impellers every two years. No problems yet. No temperature creep at full throttle, holds 175. Cruise at 1850 rpm, 16-19 kts as fuel burns off.

You don't want to overheat a 71 either.

Don't be afraid of these engines. Run them until they drop!

 

[SKYCHENEY]

Re: Fuel burn 45’ vs 53’

I now have about 30 years experience with 550 hp 6V-92TA Detroit repowers. They have been almost flawless, far better than my 8V-71Ns were (including the Allison transmissions). They don't even leak oil!

I am aware of the overheat problem but have redundant temperature and flow alarms, change impellers every two years. No problems yet. No temperature creep at full throttle, holds 175. Cruise at 1850 rpm, 16-19 kts as fuel burns off.

You don't want to overheat a 71 either.

Don't be afraid of these engines. Run them until they drop!

I have had exactly the same experience with my 6v92's. After 37 years and 5000hrs, they were still running just fine when I repowered.

 

[Hookedup2407]

Re: Fuel burn 45’ vs 53’

I’ll take the 24 holes over turbo and intercooler problems.

TA- After-cooled a little better than Inter-cooled but understood

 

[Hookedup2407]

Re: Fuel burn 45’ vs 53’

I now have about 30 years experience with 550 hp 6V-92TA Detroit repowers. They have been almost flawless, far better than my 8V-71Ns were (including the Allison transmissions). They don't even leak oil! I am aware of the overheat problem but have redundant temperature and flow alarms, change impellers every two years. No problems yet. No temperature creep at full throttle, holds 175. Cruise at 1850 rpm, 16-19 kts as fuel burns off. You don't want to overheat a 71 either. Don't be afraid of these engines. Run them until they drop!

Thanks for the input.. can you elaborate on the flow alarms?

 

[rsmith]

Re: Fuel burn 45’ vs 53’

You didn’t say what type of charter you were going to run or how far. In Cape May I used to run 70nm to fish here in Florida I only run 11. Makes a big difference. If you’re doing day charters with 6 passengers and 2 crew the big cockpit of the 53 is a big plus.

 

[jim rosenthal]

Re: Fuel burn 45’ vs 53’

Assuming close to equal fuel burn, wouldn't you want the bigger, heavier boat and larger cockpit?

I have never owned 92 series DDs, only 71s, but I think 92s are more sensitive to overheating because of their rubber sealing rings and wet liners.

 

[Hookedup2407]

Re: Fuel burn 45’ vs 53’

You didn’t say what type of charter you were going to run or how far. In Cape May I used to run 70nm to fish here in Florida I only run 11. Makes a big difference. If you’re doing day charters with 6 passengers and 2 crew the big cockpit of the 53 is a big plus.

Yes my bad.. South FL. 1 mile to the reef.. really only turn them up to blow out them out on the way in. or to get through the nasty inlet. I am currently running the 53’ now with an opportunity to own it if i choose.. Right now i burn about 27gallons on average with the 53 on a 1/2 day.. my last boat with Cummins 6CTA i would burn an average of 14gallons on a 1/2 day. 95% of use will be at trolling speeds.. the extra room on the 53 is great! Especially with 6 passengers, but there are a lot of factors that take the 53’ out of the picture when it comes to pricing trips and overall maintenance costs.. i have always said that 42-48ft with a pair of inline 6 motors is the ideal charter boat.. the 53 obviously doesn’t fit that mold. I am putting both boats down on black and white to weigh the pros and cons of each. My guess is the 6v92 will be close to what my old 6CTAs burnt in fuel.. at the end of the year it equates to a 15k$ difference in fuel burn, before i even start thinking about MOH

 

[jim rosenthal]

Re: Fuel burn 45’ vs 53’

Cummins B and C sixes are very economical. I wonder if they would burn quite a bit less than 6v-92TAs- I suspect so, at any rate.

 

[Hookedup2407]

Re: Fuel burn 45’ vs 53’

Cummins B and C sixes are very economical. I wonder if they would burn quite a bit less than 6v-92TAs- I suspect so, at any rate.

Yes I’m sure the CTAs are more efficient opened up.. less displacement 8.4 vs 9.3 and less HP as well. But still closer than a 12v71 or at least in the same ballpark

 

[rsmith]

Re: Fuel burn 45’ vs 53’

Yes I’m sure the CTAs are more efficient opened up.. less displacement 8.4 vs 9.3 and less HP as well. But still closer than a 12v71 or at least in the same ballpark

In the real world with actual documented numbers anyone who’s honest will admit increases in efficiency are very small. In the end it takes X amount of energy to move a hull through the water.

 

[Boatsb]

Re: Fuel burn 45’ vs 53’

In a 53 a QSM is minimum. That's a heavy boat for a c series.

 

[Cricket]

Re: Fuel burn 45’ vs 53’

For me it wouldn't matter if it was 1 or 70 miles there wouldn't be any 92 series engines involved, been there done that.