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Old 08-08-2019, 03:58 AM   #1
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Trawler Compromise

Hi, I have been lurking on this forum for many months gleaning a great deal of valuable information, things are now becoming real so thought it time to register and ask for help from the collective knowledge for my specific situation.

Like most I am on a budget and a further challenge is I am based in the UK where the availability of project boats and bargains are rare. It is clear that the perfect vessel will be a full displacement single engined trawler for extended passage making, it is also clear that I will have to compromise.

I believe have found a compromise boat, it is steel, 50ft, semi disacement and in a flybridge/ motor yacht style with twin engines.

Travelling at displacement speeds with this hull form is of course possible although not as Good as the full displacement hull but stabilisers will help. The fact the construction is steel will also help with stability. The vessel was originally built for long distance cruising with large fuel tanks etc. The hull design has been used on trawler style yachts but in this instance a motor yacht style superstructure is present.

My main question is around the running costs, with twin 220hp Perkins I have calculated or at least learnt from various forums that the fuel usage will be 5 gallons per hr for both engines together . The questions are do we believe this fuel usage assumption to be correct? Would it be more efficient to run one engine at a time? Could I swap out the engines for two more efficient ones or even a more efficient main engine and a wing engine?

I would value all advice on my situation, please remember that it is not an ideal world and I am compromising, I am trying to find a work around, a way to start long distance passage making without buying a nordhavn or similar.

The plan moving forward is to buy a boat in the next 6 months and over the next 5 years bring it up to standard, improve our skills with some longer passages before eventually becoming full time liveaboards, the first big trip will be the European Loop, then across to the caribbean before doing the American loop then Panama and who knows.

The vessel I am looking at is capable of the loops in terms of air and water drafts.

Many thanks in advance for your comments.
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Old 08-08-2019, 04:29 AM   #2
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" Could I swap out the engines for two more efficient ones or even a more efficient main engine and a wing engine?"

You could , anything is possible , but it would be so expensive its far cheaper to just run both engines and cruise at the sq rt of the LWL. Maybe 7K.

If you contemplate traveling , remember there are places where the taxes on fuel are minor, plan well and fill up where its cheap.
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Old 08-08-2019, 06:26 AM   #3
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The length of the vessel would help as far as fuel burn estimate. I did an engine swap on my boat and feel that it has paid for itself. That said, i did much of the labor myself, was able to sell my old motor which was much bigger for a new smaller model that the dealer wanted to clear out. My out of pocket was $10,000 plus all my time. In your situation with 2 engines that may be worth a lot less and paying to have the work done, you could spend 4 to 10 times as much. Better to invest the money elsewhere as you would never recover it with fuel savings.

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Old 08-08-2019, 07:23 AM   #4
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...with twin 220hp Perkins I have calculated or at least learnt from various forums that the fuel usage will be 5 gallons per hr for both engines together .
I'd like to confirm this statement. 1 gallon of fuel produces around 19 hp for 1 hour. So 5 gph for both engines is 2.5 gph per engine or a little less than 50 hp being produced per engine. So are you estimating using 50 hp of your available 220hp per engine for cruising?

That's certainly doable, I just wanted to make sure you were calculating this correctly.

Oh - and edited to add: I applaud your reasonable consideration for compromise. I chuckle when I hear people talking about the perfect boat. I think a boat is a million compromises all welded, bolted, and screwed together. Best of luck.
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Old 08-08-2019, 08:12 AM   #5
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Originally Posted by ScullyRN View Post
Hi, I have been lurking on this forum for many months gleaning a great deal of valuable information, things are now becoming real so thought it time to register and ask for help from the collective knowledge for my specific situation.

Like most I am on a budget and a further challenge is I am based in the UK where the availability of project boats and bargains are rare. It is clear that the perfect vessel will be a full displacement single engined trawler for extended passage making, it is also clear that I will have to compromise.

I believe have found a compromise boat, it is steel, 50ft, semi disacement and in a flybridge/ motor yacht style with twin engines.

Travelling at displacement speeds with this hull form is of course possible although not as Good as the full displacement hull but stabilisers will help. The fact the construction is steel will also help with stability. The vessel was originally built for long distance cruising with large fuel tanks etc. The hull design has been used on trawler style yachts but in this instance a motor yacht style superstructure is present.

My main question is around the running costs, with twin 220hp Perkins I have calculated or at least learnt from various forums that the fuel usage will be 5 gallons per hr for both engines together . The questions are do we believe this fuel usage assumption to be correct? Would it be more efficient to run one engine at a time? Could I swap out the engines for two more efficient ones or even a more efficient main engine and a wing engine?

I would value all advice on my situation, please remember that it is not an ideal world and I am compromising, I am trying to find a work around, a way to start long distance passage making without buying a nordhavn or similar.

The plan moving forward is to buy a boat in the next 6 months and over the next 5 years bring it up to standard, improve our skills with some longer passages before eventually becoming full time liveaboards, the first big trip will be the European Loop, then across to the caribbean before doing the American loop then Panama and who knows.

The vessel I am looking at is capable of the loops in terms of air and water drafts.

Many thanks in advance for your comments.
May I please request you answer a most impertinent question ... exactly how much money $$$$ will your 'budget' stretch to ?
Why I ask this is why all this compromise from single engine FD to twin engine SD ?
You say 'project' boat and 'bargain' and '5 years to bring it up to standard'.
I say save yourself a lot of trouble, expense and anguish and go find a KadeyKrogen 42 like Richard's Dauntless that will do everything you dreamed of and more RIGHT NOW.
Learn how to drive it over the next 5 years then do your dream. If you decide that being a blue water sailer isn't you after a few years you can sell it and stand a real good chance of getting your money back. I can't imagine a bargain or project boat will ever be anything but an expensive 'hole in the water'.
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Old 08-08-2019, 08:39 AM   #6
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Thank you for the quick replies, it seems the consensus is to retain the current engines and run at displacement speed approx 7 knts for a 50ft vessel - thank you.

Any thoughts on the Semi Displacement Hull for long passages, is it an acceptable compromise considering it is a heavy steel hull and I will install some stabilisation?
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Old 08-08-2019, 08:51 AM   #7
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May I please request you answer a most impertinent question ... exactly how much money $$$$ will your 'budget' stretch to ?
Why I ask this is why all this compromise from single engine FD to twin engine SD ?
You say 'project' boat and 'bargain' and '5 years to bring it up to standard'.
I say save yourself a lot of trouble, expense and anguish and go find a KadeyKrogen 42 like Richard's Dauntless that will do everything you dreamed of and more RIGHT NOW.
Learn how to drive it over the next 5 years then do your dream. If you decide that being a blue water sailer isn't you after a few years you can sell it and stand a real good chance of getting your money back. I can't imagine a bargain or project boat will ever be anything but an expensive 'hole in the water'.
Impertinent but important... I have around £120,000 to spend right now which I hope will get me on the water and then over the next 5 years I will invest more and bring it to a standard ready for the Blue Water. Unfortunately in the UK we don't have a great choice of second hand boats, I have just done a quick search for Kadey Krogen and there are none for sale on the more popular UK sales sites. I have seriously considered heading stateside to purchase and then ship it over, it doesnt really save any money but as mentioned there is a lot more choice over the pond.

The boat I have found is Steel, 30 years old and structurally and mechanically in very good condition - seems to have been used for a couple of seasons early on and then just maintained. The electronics and internal fittings are pretty dated so will all need changing. My thought was it will have me on the water for well below £120k and I can then bring everything up to standard.
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Old 08-08-2019, 09:02 AM   #8
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I'd like to confirm this statement. 1 gallon of fuel produces around 19 hp for 1 hour. So 5 gph for both engines is 2.5 gph per engine or a little less than 50 hp being produced per engine. So are you estimating using 50 hp of your available 220hp per engine for cruising?

That's certainly doable, I just wanted to make sure you were calculating this correctly.

Oh - and edited to add: I applaud your reasonable consideration for compromise. I chuckle when I hear people talking about the perfect boat. I think a boat is a million compromises all welded, bolted, and screwed together. Best of luck.
I am not sure it has been calculated correctly!!! I have struggled to find the information, this came from a post on another forum from a guy with the same engines and similar sized boat. He was saying 5gph @ 1600/1800rpm 10knts. Any advise or experience you have with this would certainly be welcome.
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Old 08-08-2019, 10:09 AM   #9
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We have a 41’ semi displacement boat with twin SP225 Lehmans. We generally cruise about 8.5 knots and burn about 6 to 7 gallons per hour. It would be more economical if we were to slow down to 7 knots but we like doing 8.5 and the fuel burn is acceptable to us. Our engines are pretty close to the ones you are referring to so I would think that your fuel burn would be similar except maybe that your boat is probably quite a bit heavier than ours. Ours is around 28,000 pounds as far as we can tell.
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Old 08-08-2019, 10:28 AM   #10
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Great information thank you, this vessel is around 28tons
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Old 08-08-2019, 12:41 PM   #11
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I am not sure it has been calculated correctly!!! I have struggled to find the information, this came from a post on another forum from a guy with the same engines and similar sized boat. He was saying 5gph @ 1600/1800rpm 10knts. Any advise or experience you have with this would certainly be welcome.
Those numbers don't ring true. For a 50' boat, 10 knots will be pushing a lot of water, certainly not on plane. I might believe 5 GPH for each engine. Don't think you can push a 50' boat at 10 knots with 100 HP.

My 45' boat (50' LOA) at about 45,000 pounds will go 7 knots at 2 GPH, 8 knots at 3.7 GPH, can't reach 9 knots with the 135 HP engine.

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Old 08-08-2019, 03:00 PM   #12
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Three comments:

1-You say the boat is in good shape and structurally sound. How have you determined that? Are you a marine surveyor or did you hire one? I know I could definitely not tell you if a steel boat is sound or not.

2-I think your fuel consumption numbers are off as others have said. I also wouldn't consider replacing the engines if they're in good condition.

3-You say it's steel semi-displacement. I'm not saying that's impossible but it's very contrary to most steel construction and would be extremely rare. What do you base that conclusion on? I suspect it's a displacement hull with just the power to push it faster than most similar displacement boats but lacking the characteristics of a semi-displacement hull.
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Old 08-08-2019, 03:50 PM   #13
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Here are some rules of thumb and observations on your proposed steel boat.


Your boat weighs about 60,000 lbs and is 50' long. A displacement hull (yours isn't) requires about 1.5 hp per 10,000 lbs to go to displacement speed. This rule of thumb has been proved by data in the Bebe/Leishman book. Semi displacement hulls take about 1.5 times much fuel as displacement hull to reach hull speed. So your boat will require 1.5*1.5*6= 135 hp at hull speed. Your LWL is about 46' so your displacement speed is about 9 kts. You should be able to cut that in half at 7 kts or about 70 hp. Two generation old high output diesel engines make about 15 hp per gpm at the low to mid hp range, so your fuel consumption at 7kts should be about 4.7 gph.


So your 5 gph estimate is in the ball park.


As others have said, keep the engines, run them slow and enjoy decent fuel economy. Will 5 gph at 7 kts get you where you want to go?


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Old 08-08-2019, 04:58 PM   #14
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Three comments:

1-You say the boat is in good shape and structurally sound. How have you determined that? Are you a marine surveyor or did you hire one? I know I could definitely not tell you if a steel boat is sound or not.

2-I think your fuel consumption numbers are off as others have said. I also wouldn't consider replacing the engines if they're in good condition.

3-You say it's steel semi-displacement. I'm not saying that's impossible but it's very contrary to most steel construction and would be extremely rare. What do you base that conclusion on? I suspect it's a displacement hull with just the power to push it faster than most similar displacement boats but lacking the characteristics of a semi-displacement hull.
Three responses:

1. Valuable point, I have a survey from 4 years ago which is good, clearly 4 years in salt water is a long time I have lifted every hatch possible and my untrained eye see's no issues with the original epoxy coating on the inside, the engine runs up fine a little smoke on startup but clears after a few mins and a comprehensive folder of reciepts for work and servicing. I will use a professional surveyor before any money is exchanged, I have spoken with one and have a quote.

2. It is great that everyone agrees reference leaving the engines, I think we are getting close to understanding the consumption figures. My concern was the sheer volume of fuel required for some extended passages however I was translating costs to what we pay in the UK, I now realise that with large tanks I can pick and choose where to fill up and there are a lot better places than the UK so it is not such a concern now.

3. I base the assumption that it is semi displacement from the original designs by Bruce Roberts, this was constructed by a professional boat yard and was inspected by Bruce Roberts so i am confident in the build standard in this case, I know that a good number of Bruce Roberts designs are home built and of questionable quality. I agree that a steel vessel of this size would need an enormous amount of power to plane, I doubt the current engines would push the boat over the hump and I am happy with displacement speeds.

Great feedback thank you.
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Old 08-08-2019, 05:08 PM   #15
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Here are some rules of thumb and observations on your proposed steel boat.


Your boat weighs about 60,000 lbs and is 50' long. A displacement hull (yours isn't) requires about 1.5 hp per 10,000 lbs to go to displacement speed. This rule of thumb has been proved by data in the Bebe/Leishman book. Semi displacement hulls take about 1.5 times much fuel as displacement hull to reach hull speed. So your boat will require 1.5*1.5*6= 135 hp at hull speed. Your LWL is about 46' so your displacement speed is about 9 kts. You should be able to cut that in half at 7 kts or about 70 hp. Two generation old high output diesel engines make about 15 hp per gpm at the low to mid hp range, so your fuel consumption at 7kts should be about 4.7 gph.


So your 5 gph estimate is in the ball park.


As others have said, keep the engines, run them slow and enjoy decent fuel economy. Will 5 gph at 7 kts get you where you want to go?


David
Thanks David - this is really good information, I am happy to run slow on the long passages and realising fuel is cheaper in pretty much every other country than the UK is great. In the UK 5gph equates to about £30 which is fine for local passages and runs across to France understanding on a long passage per 24hrs would be £720 which soon mounts up. It will be fine when I am in cheaper countries .

Thank you for breaking down your calculations.
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Old 08-08-2019, 09:46 PM   #16
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That boat will not get on top of the water , period. It might be full displacement or semi displacement. I would be shocked if you could get it to 10 kt. The 5 gallons per hour sounds reasonable at slow rpm. You should be in the 1.5 mpg range, not bad for a big boat.

Forget about running on one engine. You would not save anything at all and unless you have a transmission built to "free wheel" you will ruin it. If you lock up that shaft you are dragging a 25 inch (or so) prop through the water, adding a lot of drag and eating a lot of fuel.

Unless you really get lucky it will cost you a minimum of $50,000 to repower, probably more like $75,000. Trying to change to a single screw set up will be just about as expensive. You save the cost of an engine and tranny but add it right back in reconfiguring the engine, rudder and balance issue. You can buy almost 20,000 gallons of diesel fuel for the cost of re powering.

Most boat purchases require some amount of compromise but it sounds like you are making more compromises than you need to. Shop around a little more. I suspect that even in a tight market when the brokers learn you are a serious buyer with cash or financing lined up some good boats will start appearing.

Good Luck

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Old 08-09-2019, 05:55 AM   #17
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"Any thoughts on the Semi Displacement Hull for long passages, is it an acceptable compromise considering it is a heavy steel hull and I will install some stabilisation?"

Adding a stabelizing system will be complex and costly. The hull might require beefing up where the system is mounted. Even flopper stoppers are a system that requires good structure in a specific location.

I would cruise the boat and use a speed increase to see if that , or a minor course change would not give an acceptable ride.

An extra bit of even highly taxes diesel is a lot easier than a vessel refit.


19HP from a gallon of diesel can be done , but it is usually more like 15 as the engine is not opertating at cruise at its best RPM .
Near the torque peak is best you can do, but with out a CPP usually the prop is way too small,and lacks pitch, esp in a semi displacement boat.
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Old 08-16-2019, 02:06 PM   #18
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Expect 17 hp per gallon (US) run those 6 cylinder Perkins at 1600 rpm. What is considered hull speed is 1.34 times the square root of the waterline length; this not an efficient speed. It is a maximum speed. Expect 1.15 times the square root of the waterline length as your cruising speed, in your case 7.0 knots is it. As for open sea cruising what really matters is double decking and deck height. doubled decking is not feasible in vessels less than 60 feet, just too much height above the center of gravity. A single level with only the pilot house raised above the engine room is most seaworthy. Pole stabilization is a must for long offshore cruising (and they are great at anchor), but they cost you 1/2 knots in speed or more fuel. Twinn engines are actually a plus. They do not compromise efficiency as some would believe. They add greatly to close quarters maneuvering. They provide redundacy. They operate in the shadow of the center fat cross section and higher above the keel with less likely hood of striking the bottom than a single screw equivalent vessel (in a displacement designed vessel, not a flat bottomed vessel). So how do i know this? I have a twin 115 hp shrimp trawler hull. Built as an expedition vessel in 1980. Currently I have 65,000 hours underway on the engines. Power consumption is about 58 hp per side at 1375 rpm (4-71 Detroit's indestructible. Never had the heads off at 65,000 hours), 7 knots with stabilization down and towing a 7 meter heavy full displacement dingy. About 1 mile to the gallon fully loaded at 165,000 lbs.. I have had this vessel in continuous operation for 38 years. Constantly in use in the Bahamas for remote expedition dive excursions, so these numbers are real. PS: registered volumetric tons are not the same as displacement tons. Only use displacement tons for your calculations. The tonnage listed on your registration is not the displacement tonnage. Is is basically a taxable tonnage for cargo and is not directly related to the displacement tonnage. Hope this helps. -Captain Dan-
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Old 08-16-2019, 02:43 PM   #19
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Captain Dan very good post.
Reality has finally arrived.
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Old 08-16-2019, 02:44 PM   #20
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Scully; Welcome! and for better or worse you've entered a site where there are lots of strong opinions, which you can take or leave... or at least take with a grain of salt
Congrats on an exciting time, its a great feeling being on the precipice of a boat purchase.
If you can hit around 5 GPH, that is a pretty efficient number for a large trawler, especially steel. Run that number against your total fuel tank capacity and see if that gets you passagemaking ability for the future trips you're planning.
You say there's limited used boat availability there, I'm curious because you're pretty close to Scandinavian waters and they make some pretty incredible products, anything in the Denmark region perhaps?
As for running a twin on one engine: typically not good unless a boat has been setup to do this. One of the key issues is if a boat has certain dripless shaft seals that are watercooled reliant on engine power. Therefore if one engine isn't running, you can end up with a spinning shaft that is not being cooled. There is a way to setup crossover plumbing from one shaft to the other but i don't think this is common.
Finally on stabilization: it kind of depends on how she behaves now; hopefully you will get a sea trial where you'll get a feel for her out on the water, good luck!
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