$50K and 1 gph?

Something to consider is the theoretical hull speed of the vessel, which can vary greatly from vessel to vessel

√ LWL * 1.34 = Theoretical Hull Speed.

Part of the key is the LWL (Length at Waterline), not the vessel length (LOA). LWL is typically a few feet shorter than LOA. Model numbers are rarely close to either LOA or LWL.

In order to get a Hull Speed of 8kts you would need an LWL => 36 ft.

A 36 ft boat with an LWL of 33ft would have a theoretical hull speed of 7.69 kts. Exceeding hull speed increases fuel burn exponentially as it is increased.

Since nautical charts are in Nautical Miles, speed (including this calculation) is based on knots, not Kilometers and not Miles Per Hour.

Something to consider when doing real-world calculations.

HeadedToTexas said:

unless you're willing to brave the heat and humidity, air conditioning requires at least 120 VAC. Do many folks cruise the Loop without AC?

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Somewhat depends on how you do the loop. If you spend the winter in the south, the spring heading north, the summer on the Trent-Severn and Great Lakes, and the fall heading south down the Mississippi and the Tenn-Tom, you can minimize the need for AC but I suspect you will still encounter several days you wished you had AC and several days you wish you had a heater. You just don't get perfect weather all the time.

I returned from Florida with my new to me 2003 OA 456, with twin cummins 6BTA putting out 315 SAE hp. We typically ran about eight knots, but frequently popped her to nine and 9.5. Manatee zones and no wakes put us at 5 - 6 knots. We averaged 4 gph which figures out to a bit more than 2 gal/m when I did the final computation.

Also, I have a bit more drag than the conventional boat as a result of pushing stabilizers through the water.

Gordon

On the hard

Simi 60 said:

FPB's, Artnautica's and the like

If wanting comfort, REAL comfort in a passagemaker, Waterline length and lots of it , low weight, low windage and low whetted surface area is everything

SetSail » FPB 64

https://www.morganscloud.com/2015/01/10/a-real-sailors-motorboat-launched/

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The boat pictured at the top is currently on the hard after ripping out a stabilizer on the ICW. It was at Cobbs marina (nrofolk, va) last week for any local folks who want to see it.

Gordon

Oshrew wrote;
"A 36 ft boat with an LWL of 33ft would have a theoretical hull speed of 7.69 kts. Exceeding hull speed increases fuel burn exponentially as it is increased."

Actually it should be "getting near hull speed" The "brick wall" as it's called most often starts well below hull speed. About 3/4 of a knot below on a 35' boat .. approx. Very close to 7 knots would be an ideal econocruise speed for the above boat.

I run my FD 30' boat .85 of a knot below hull speed 99% of the time. Of course SD boats can go much faster the good economy for a trawler is 1/2 a knot to 1.25 knots depending on boat length. So hull speed is not the speed to go for economy .. think less than HS.

READY2GO said:

As others have said fuel is not your biggest expense, don't let it decide your boat choice. Buy a boat is comfortable to you regardless of fuel burn, set it up to live on at anchor. Save your money on marina usage instead of fuel and you will be happier (my opinion).

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What he said.
$1300/mth in Marina fees for my boat buys more fuel than I would use.
We'll be very comfortable living on the hook at nearby deserted islands.

Gordon J said:

The boat pictured at the top is currently on the hard after ripping out a stabilizer on the ICW.

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Compelling argument for Paravanes.
That and the $40k in difference.

Nomad Willy said:

So hull speed is not the speed to go for economy .. think less than HS.

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Yep. More of a "maximum slow" than a target to shoot for.

Our example illustrates:
- 800 RPMs, 6.5 kts, 1.2 GPH, 2,93 NMPG
- 900 RPMs, 7.0 kts, 3.0 GPH, 2.35 NMPG
- 1200 RPMs, 8.9 kts, 5.8 GPH, 1.53 NMPG (approx. our theoretical max hull speed)

Not perfect comparison, since our hull form is different from FD, but makes the point I think.

-Chris

READY2GO said:

As others have said fuel is not your biggest expense, don't let it decide your boat choice. Buy a boat is comfortable to you regardless of fuel burn, set it up to live on at anchor. Save your money on marina usage instead of fuel and you will be happier (my opinion).

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Thanks for all the input, folks. Great stuff. I am convinced that fuel consumption is secondary. If I stay in the sub-40' market and run a single Lehman 120 or 135, burn rate should be quite comfortable regardless.

How about this corollary question. Is a diesel generator the best way to make enough AC to run an AC when needed? I've spent a lot of summer time boon docking in RVs and virtually never run air conditioning (or the generator). On those rare times, can AC be run off solar/wind/alternator charged batteries?

HeadedToTexas said:

Thanks for all the input, folks. Great stuff. I am convinced that fuel consumption is secondary. If I stay in the sub-40' market and run a single Lehman 120 or 135, burn rate should be quite comfortable regardless.

How about this corollary question. Is a diesel generator the best way to make enough AC to run an AC when needed? I've spent a lot of summer time boon docking in RVs and virtually never run air conditioning (or the generator). On those rare times, can AC be run off solar/wind/alternator charged batteries?

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There are some folks that have rigged up larger alternators and inverters to run an AC unit while underway without running the genset - however for most purposes you are just better off running the genset - unless you are putting on major hours underway you won't ever recoup the increased costs associated with the inverter/alternator/associated switching. Solar/Wind won't put out near enough juice for an AC unit.

As to air conditioning on the loop. We are addicted to air conditioning, don't leave home without it. However, I see no problem doing the loop without it. The schedule most follow puts you in the perfect climates for the time of year and generally very moderate conditions.

devorenm said:

There are some folks that have rigged up larger alternators and inverters to run an AC unit while underway without running the genset - however for most purposes you are just better off running the genset - unless you are putting on major hours underway you won't ever recoup the increased costs associated with the inverter/alternator/associated switching. Solar/Wind won't put out near enough juice for an AC unit.

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OH MAN!!!!! Somebody gets it!!!! Listen to this guy!!!! I am absolutely baffled by the measures and expense that people will go through simply to avoid running a generator. A generator, when compared to wind/solar/batteries/inverter/controllers/regulators/etc is SO much simpler than all that other crap. And cheaper too!!!!!!

Baker said:

OH MAN!!!!! Somebody gets it!!!! Listen to this guy!!!! I am absolutely baffled by the measures and expense that people will go through simply to avoid running a generator. A generator, when compared to wind/solar/batteries/inverter/controllers/regulators/etc is SO much simpler than all that other crap. And cheaper too!!!!!!

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You are probably right for a boat used on some weekends and the occasional longer trip.
Different kettle of fish altogether for an actual live-aboard off the hook.

When under way, I almost never run the gen and AC. Just open up the boat and it is comfortable even on a hot day. But sleeping on the hook in summer, man that AC is appreciated.

ranger42c said:

Yep. More of a "maximum slow" than a target to shoot for.

Our example illustrates:
- 800 RPMs, 6.5 kts, 1.2 GPH, 2,93 NMPG
- 900 RPMs, 7.0 kts, 3.0 GPH, 2.35 NMPG
- 1200 RPMs, 8.9 kts, 5.8 GPH, 1.53 NMPG (approx. our theoretical max hull speed)

Not perfect comparison, since our hull form is different from FD, but makes the point I think.

-Chris

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Chris, did you mean 6.5 knts @ 2.1 gph?

Ah. Good catch. Thanks. Typo in my note 27, and copied again in #38. Should have read 800 RPMs, 6.5 kts, 2.2 GPH, and 2.93 NMPG.


And again, these are all taken from the published nominal fuel consumption curves compared to my bi-directional speed tests, not from on-board fuel flow instrumentation.


-Chris

Most of the Willard’s under 40 ft Fall in this category

Hehe, among my first posts here. 2016! Good stuff. I'm pretty happy at 4 gph now.

26 foot Albin, single F.L. 120, 1.5 gph at about 6 - 7 knots. (1750 rpm)

I never run the genny while underway. Usually no reason for the extra noise.

Yes, you want a genny, heat and air on the Loop. Also bikes, a cooler for ice, a dinghy, maybe kayaks.

pete

I have the Lehman 80hp 4 cyl. and can get 1 gph at 6 knots. 30 feet and all the room my wife and I need.

Something not often discussed in the gph threads is the condition of your (actually, the boat's) bottom. When travelling in an area where one can go between fresh and salt every couple of days, the bottom stays fairly clean. In constant fresh water (in the summer) a trip over the side with a brush isn't too difficult. In salt, it's not that easy or fun in northern waters. A mildly fouled bottom can make a 10% increase in your fuel usage. When hauling along a barnacle ranch, it's likely even higher usage and lower speed.

My fuel usage above 8 knots drops to zero (because I can't go that fast).

In 1992 I had a Hunter 34 sailboat. It came with a Yanmar 3GM 24hp diesel. I ran the boat at 6kts and burned 2/3 a gallon per hour. This would equate to 8 nautical miles per gallon.

A friend had a Nordic Tug 26’. He ran 6.5kts but burned 1 gal per hour. I suspect if he slowed to 5.5 he could have reached 8kts per gallon but his comment was always “Why?”.

When I Looped in 2017, fuel was cheaper and I was cruising 7 knots at 2 GPH (3.5 MPG).

With higher fuel prices in the last couple of years, I have slowed down to 6 knots at 1.2 GPH (5 MPG).

Certainly can't complain about the fuel economy.

Ted

I got 4.0 nmpg looping on my Mainship 34, and 4.5 nmpg looping on Escapade.

6.5 knots is 1 gph, but a little slow for me most of the time. 8 knots is under 2 gph.

49' WLL, 35k displacement, JD 135

Simi 60 said:

Sweet baby Jebus, 25ft?

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That had me chuckling. Although I do agree 25ft is a little small for me too Simi, not everyone needs the elbow room that you have on your palatial yacht.

Now, we may wish for it, but...