Boat design vs actual use?

[ranger58sb]

I know nothing about sportfish types, just how thirsty is a typical 40' sportfish at speed?
Bruce

Depends, but ours nominally gulps about 27 GPH (total) at 2200 RPMs, which is about 400 RPMs below WOT and gets us about 20 Kts, depending on bottom condition and sea states. That'd rise to about 35 GPH at 2400, about 23 kts, depending. Approaches .7 NMPG...

SERIOUS offshore sportfishers, though, would be running much bigger engines (Viking often installs V-10 or larger MANs, several use MTUs or much larger Cats, etc.) and they'd be looking for 30 kts cruise minimum. And there are still lots of huge DDs out there. I dunno much about individual specs on all those, but I'd guess more like at least twice what we burn.

-Chris

 

[BandB]

Depends, but ours nominally gulps about 27 GPH (total) at 2200 RPMs, which is about 400 RPMs below WOT and gets us about 20 Kts, depending on bottom condition and sea states. That'd rise to about 35 GPH at 2400, about 23 kts, depending. Approaches .7 NMPG...

SERIOUS offshore sportfishers, though, would be running much bigger engines (Viking often installs V-10 or larger MANs, several use MTUs or much larger Cats, etc.) and they'd be looking for 30 kts cruise minimum. And there are still lots of huge DDs out there. I dunno much about individual specs on all those, but I'd guess more like at least twice what we burn.

-Chris

Yes, most Hatteras get anywhere from 0.3 to 0.4 nmpg at cruising speeds.

 

[Bruce B]

Interesting. That would be 2 to 3 times the amount of fuel used by the boat we are purchasing although it would be faster.
I love the look of a sportfish, it looks so purposeful. If only I fished...
Bruce

 

[bayview]

Interesting. That would be 2 to 3 times the amount of fuel used by the boat we are purchasing although it would be faster.
I love the look of a sportfish, it looks so purposeful. If only I fished...
Bruce

Seems people have a hard time understanding that fuel use is determined by how fast the boat moves and how heavy it is. Fuel use is not a fixed quantity and is heavily dependent on the operator. Similar weight boats will use similar fuel at the same speed..

 

[Bruce B]

Seems people have a hard time understanding that fuel use is determined by how fast the boat moves and how heavy it is. Fuel use is not a fixed quantity and is heavily dependent on the operator. Similar weight boats will use similar fuel at the same speed..

That is pretty easy to see actually, I'm simply unfamiliar with the benchmarks.
Just trying to develop a sense of the range of possibilities.
Bruce

 

[psneeld]

True about fuel usage, but for me to get my old 37 foot sport fish to approach the same nmpg that my trawler would get, I would have to shut down an engine and idle the other one all day long. The sportfish would still be a knot or so slower which over 2500 miles of cruising is huge in terms of time and engine use that is questionable.

There are many "what ifs" and "sure you cans" in boating... but you have to make the compromise decision and draw the line someplace.

 

[LarryM]

Interesting. That would be 2 to 3 times the amount of fuel used by the boat we are purchasing although it would be faster.
I love the look of a sportfish, it looks so purposeful. If only I fished...
Bruce

"Purposful" is a great a great description! The Coastal is a fairly light boat at about 18,000# fully loaded. With diesel power, they get around 1.2 NMPG at 20+ KT cruise and somewhere around .75-.80 NMPG at WOT, still not so bad in my estimation. What a difference in speed and range though. A completely new world for me.

 

[Art]

Interesting topic... a boat's nmpg fuel use.


I find that speeds somewhat over hull speed (for SD or P hulls) that may be discussed by boat owners usually amounts to approximately 1 nmpg. Unless speed begins to get into the 20 nmph range and of course when it is 30 nmph or over; then nmpg drops into or below the 0.5 mnpg range. Of course mnpg at hull speed or below for D, SD or P hulls begins to create some pretty good boat mirage per gallon. Some D-hull boat owners report up to or even a little over 4 nmpg.


If our (loaded) Tolly (with P-hull) is cruised at a comfortable 16/17 knots on full plane she gets 1 nmpg. At just below hull speed (i.e. at 6.5 to 7 knots - hull speed is calced at 7.58 knots) running both engines she gets just under 2 nmpg. At well below hull speed (4.5 to 5 knots) running only one engine she comes real close to 3 nmpg. I do like having the 16/17 knot full plane cruise speed to get where we want fairly quickly. At her top speed of 22/23 knots I can just imagine the 0.5 nmpg rate would come into play... don't ever intend to find out, cause that WOT level I only use for short couple of minute bursts during engine testing or to get quickly out of trouble if needed around misguided skippers mishandling their boats. For a medical emergency I can see running at or near WOT for whatever time is required. Luckily that particularly disturbing need to continue top speed over longer time span has never arisen to this point in time. But, if it did - I could care less what mnpg was the outcome!


All in all - The fuel use/rate experienced (allowed) on a boat is usually directly proportional the thickness of wallet as well as fuel costs during that juncture of history.

 

[Art]

"Purposful" is a great a great description! The Coastal is a fairly light boat at about 18,000# fully loaded. With diesel power, they get around 1.2 NMPG at 20+ KT cruise and somewhere around .75-.80 NMPG at WOT, still not so bad in my estimation. What a difference in speed and range though. A completely new world for me.

Larry - What speed is reached at WOT?? - Thanks, Art

 

[Fletcher500]

Since the discussion has moved to fuel burn in P hulls, I will chime in.

One of the reasons I was drawn to our boat it was the hull design. The aft 1/3 portion of the hull rides on an air cushion on plane. There is a port on each side of the hull where air is drawn in at speed, by using the Venturi affect.

The boat is on plane at about 2700 and total burn is 25 Gph for both engines. This equates to about 1.1 and 23 knots depending on sea states and whether the trim tabs are working, which were not last weekend. WOt is 3550 and about 3o knots.

 

[koliver]

As side note to boat usage... and, Just For S&G...


I'd like to be seat belted into Captains seat and have about six (6) hours un restrained use of a self righting CG rescue boat. Now, that could be fun in white water!

Art:

Right you are,driving one of those boats is a lot of fun. However, before you will be sitting in the Captain's chair, you will have a lot more than 6 hrs at the helm, in the roughest of conditions, just to prove you have the skills. That represents a huge commitment of your time and a very understanding Admiral.

I began volunteering with our local RCMSAR last summer. It took till the middle of August to get a ride on the boat, where the Coxswains could get a look at my actual skills. Then it took until early October to get a ride in 2m seas and 35k winds. This ride had me sidelined until we had completed a rescue and were heading home, when I was given the helm. Up to that time, the guy with the most experience, who had also demonstrated a high level of competence at the helm, took us to the rescue site.
Since then I have been flattered by the other crew who give me the helm whenever some difficult maneuvering is contemplated. I am sure this will not be mimicked by the other new crew and they come on board, as nobody else in the group of recent recruits has the years of experience that I have.

Since early November I have been away, and the other new Crew have been training, so I will again have hill to climb, just to get back to where I was when I left. I expect to be back in the saddle Mid- April. I am not expecting my absence over the winter to work in my favour. Then there is the summer vacation time, when I will be using my own boat and ignoring call out commitments to the SAR.

And no, we don't use seatbelts in our open RIB. We have shock absorbing seats for 3 and anyone else stands and just hangs on.

 

[bayview]

fletch:

I expect that your boat weighs about 30,000# or less. Build a planing heavy aft cabin boat at the same 44' it will weight closer to 40,000# loaded and use more fuel, at speed.


All the talk about fuel and length is meaningless without weight and speed.

 

[Art]

Art:

Right you are,driving one of those boats is a lot of fun. However, before you will be sitting in the Captain's chair, you will have a lot more than 6 hrs at the helm, in the roughest of conditions, just to prove you have the skills. That represents a huge commitment of your time and a very understanding Admiral.

I began volunteering with our local RCMSAR last summer. It took till the middle of August to get a ride on the boat, where the Coxswains could get a look at my actual skills. Then it took until early October to get a ride in 2m seas and 35k winds. This ride had me sidelined until we had completed a rescue and were heading home, when I was given the helm. Up to that time, the guy with the most experience, who had also demonstrated a high level of competence at the helm, took us to the rescue site.
Since then I have been flattered by the other crew who give me the helm whenever some difficult maneuvering is contemplated. I am sure this will not be mimicked by the other new crew and they come on board, as nobody else in the group of recent recruits has the years of experience that I have.

Since early November I have been away, and the other new Crew have been training, so I will again have hill to climb, just to get back to where I was when I left. I expect to be back in the saddle Mid- April. I am not expecting my absence over the winter to work in my favour. Then there is the summer vacation time, when I will be using my own boat and ignoring call out commitments to the SAR.

And no, we don't use seatbelts in our open RIB. We have shock absorbing seats for 3 and anyone else stands and just hangs on.

Hey Keith - TY for chiming in.

Sounds like you greatly enjoyed your experiences!

Back-When! In fall/winter times, around NY, I used to take smallish fishing boats into white waters. I also during my growing decades on east coast experienced a couple of pretty hairy times in turbulent seas off the coast. I'll probably never get to experience piloting one of those self righting CG rescue boats. But, my dream lives on!! Can never blame a boater for dreaming... cause... in actuality... pleasure boating is nothing more than a dream fulfilled. And, that ain't half bad!

 

[ranger58sb]

Interesting. That would be 2 to 3 times the amount of fuel used by the boat we are purchasing although it would be faster.
I love the look of a sportfish, it looks so purposeful. If only I fished...
Bruce

Seems people have a hard time understanding that fuel use is determined by how fast the boat moves and how heavy it is. Fuel use is not a fixed quantity and is heavily dependent on the operator. Similar weight boats will use similar fuel at the same speed..

That is pretty easy to see actually, I'm simply unfamiliar with the benchmarks.
Just trying to develop a sense of the range of possibilities.
Bruce

Yep. We run slow lots more than we go fast. Usually down around 900-1200 RPMs, which can nominally average about 7-9 kts (depending on factors) and nominally around 2.35-to-1.5 NPMG.

-Chris

 

[Fletcher500]

fletch:
I expect that your boat weighs about 30,000# or less. Build a planing heavy aft cabin boat at the same 44' it will weight closer to 40,000# loaded and use more fuel, at speed.
All the talk about fuel and length is meaningless without weight and speed.

My signature has the type of boat, so someone reading my post knows its not an aft cabin.

There are other variables involved. As noted, I am getting 1.1 NMPG at cruise. That is very good, and better than most boats in the EC class.

Some of the key factors are weight, as you noted, and this boat has drives, which are more efficient than props. Also, the air cushion I previously described helps as well.

 

[Fletcher500]

I meant to type "shafts" not "props".

 

[eyschulman]

The whole "Trawler" thing gets way too much air time.
I think of it as more of a mind set than anything else. Fast, slow, single, twins, gasoline, diesel...whatever!
It is more a style of use than anything else in my book and even if your use is different than mine there are lots of overlapping issues to discuss. That is what makes this all so interesting.
Enjoy your new boat, I'm sure it will be a blast.
Bruce

This is a power boat cruisers forum no matter the misnomer on the home page. This is a point I have tried to bring attention to in the past when I wanted a definition of a recreational trawler a kind of imaginary fuzzy concept. The trawler word does get a lot of attention and has been instrumental in making the site work. Maybe the home page should read trawler and power cruising forum then everybody can be more inclusive and closer to correct.

 

[Art]

This is a power boat cruisers forum no matter the misnomer on the home page. This is a point I have tried to bring attention to in the past when I wanted a definition of a recreational trawler a kind of imaginary fuzzy concept. The trawler word does get a lot of attention and has been instrumental in making the site work. Maybe the home page should read trawler and power cruising forum then everybody can be more inclusive and closer to correct.

How bout - - > "Waterborne Fun Time Power Cruiser Pleasure Craft"

Just to get it into a BIG but true mouthful!

 

[BandB]

My signature has the type of boat, so someone reading my post knows its not an aft cabin.

Wifey B: ? I don't see a signature at all.