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Old 09-17-2017, 08:49 PM   #1
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Pros and cons of single or twin engines for GB 36s?

We're looking at GB 36s for planned Inside Passage cruise to Alaska from Washington State next year. Hoping experienced skippers will give their thoughts on a single versus twin engine model. Interested in fuel efficiency; not worried about speed except in tidal channels, but like the safety measure of a second engine.
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Old 09-17-2017, 09:03 PM   #2
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We're looking at GB 36s for planned Inside Passage cruise to Alaska from Washington State next year. Hoping experienced skippers will give their thoughts on a single versus twin engine model. Interested in fuel efficiency; not worried about speed except in tidal channels, but like the safety measure of a second engine.
Bruce - What a "fun" can o' worms to open... i.e. single - vs - twin!

I'm sure plenty will post.

There have been hundreds of posted conversations previously in this topic. Go into search feature and I'm confident you will find plenty to read.

My preference is twin screw... for a lot of reasons.

Happy Boat-Screw Daze! - Art
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Old 09-17-2017, 09:23 PM   #3
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OK, I'll start

When I first came to TF back in 2011 I realized that a old working "friend" was active here.

I called him, and we talked bigger boats since I was boat shopping. I asked him if he ever wished he had twins, since his boat has a single engine. He told me, Yes, when his engine died in a place wth a current that was pushing him against the rocks in British Columbia, and the Canadian Coast Guard had to come to his rescue.

I bought a twin engine boat soon thereafter.

That said, I have allot of sea miles under my keel and have never come into port on one engine. Prior to this I had mostly single engine gas cruisers and only had to be towed back to port once.

So...

Chose a boat you like, and if it has one engine, great. If it has two, great. If you would sleep better at night knowing you have two engines then buy a boat with two engines.

This is really a matter of personal preferance. I would be quite happy with a single engine boat. My wife would worry herself into a tizzy.

All this said a single engine boat offers a somewhat better fuel economy. How much better is open to debate. A single is 1/2 the price to maintain. A single protects your prop better in most boats.

Twin engines maneuver at the dock much better, and you always have the peace of mind in knowing that if one engine goes TU you have another.
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Old 09-17-2017, 09:29 PM   #4
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Hundreds and hundreds of trips have been made up the Inside with single screw boats.

A single screw GB 36 is a fine and capable boat that would be fine on this type of trip.

1/2 the maintenance, fuel and equipment, more room for stores and stuff.

Easy choice for me!
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Old 09-17-2017, 09:59 PM   #5
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The ER in a GB36 is quite roomy. The access between its twins is enough for two grown men. I know because a good friend had a GB36 with twins. I spent time in the ER helping him familiarize himself with all of its systems. There was no difficulty in getting at the off sides of either engine. There was lots of room left over for storage of spares, tool kit, the genset, etc.
If that ER held only one engine, access to all of the systems would be equally good, though only one grown man could be on each side rather than both in the middle.

Maintenance costs relate more to the total hp in the ER than to the no of engines. I know, because I have twin 200 hp diesels in my boat and a single 400 hp engine in my Motorhome. The Motorhome oil changes cost about the same as the pair of oil changes I do on the boat. If you buy a single impeller for the raw water pump on a 400 hp diesel, you get one that is twice the cost of the individual raw water impellers on the 200 hp engines. But those costs don't come up that frequently. Racor filter elements for the 500 series are less than for the bigger ones you need for the bigger engines. Etc.....

I have had a serious engine failure. I was able to schedule the repair for the close of the boating season, even though the failure occurred in June. On Sept 15th I took the boat in for that repair. In between I had an enjoyable 3 weeks vacation, putting the expected hours on the remaining engine, learning to come into docks on only one in all conditions, using less fuel, as without the other engine I couldn't go as fast. If I had that failure with only one engine, I would have missed the whole boating season.

Economy is determined by how fast you go, not by how many propellers are turning. If you want economy, slow down. I get 2 mpg at 8 knots. At 6.5 I get almost 4 mpg. I prefer to go 8 and continue to do so, now that I am running both engines again.
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Old 09-17-2017, 10:08 PM   #6
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If running costs are an important part of your consideration then a single screw will no doubt look like the better pick,but here's a few other advantages as well

1) A single, center-line propeller is protected by the keel and rudder. I've seen this numerous times in boat designs, and yet never gave it much thought in comparison with two, exposed props.
2) Nearly one hundred percent of the commercial fishing and work boat vessels (of all sizes) are single screw/one engine boats.
3) If you learn how to drive a boat, you can manage without fiddling with twin-engine sticks. Two words: bow thruster.
4) One engine is cheaper than two. One engine is cheaper than two. One engine is cheaper than two. Any questions?
5) As long as you carry the normal spares and some what handy this will get you out of trouble in most cases
6) Most boaters are never out of sight of land to begin with, and therefore Sea-Tow is only a call away. Before i get taken to task for that one, consider the cost (economically and emotionally) of Sea-Tow the .05% of the time you need them, versus the cost of operating the boat with two engines 100% of the time.
7) Then remember that Nordhavns cross oceans mainly with a Single Engine(although many have emergency set ups for a get home solution!)

All in all, this debate really centers on your comfort level with a single vs. twin installation. If a second engine makes you feel safer, by all means do it. If you've learned how to change water pumps, impellers, hoses and fan belts, and carry spares (all of these things should apply if you are any kind of boater), then you may just find that a single screw boat is cost-effective, reliable, and simple.

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Old 09-17-2017, 10:11 PM   #7
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There are a lot of discussions on TF about single vs twin. The points you'll hear are typically:
- (someone can correct me but I think) Twins burn around 50% more fuel (not usually 2X). Do the math...estimate your total running time hours (500?) for the trip, run the expected gph fuel consumption for single and twin, and see if the additional fuel cost is really an issue for you. There are plenty of big expenses besides fuel.
- More commercial boats, such as the ones on Deadliest Catch, run a single. But they have an engineer on board, major repair capability, etc.
- Two engines = 2X maintenance
- Single may give you more range assuming boat's total fuel capacity.
- Twin does offer a margin of safety but most debilitating engine problems are fuel related so unless you're running separate tanks they both are affected.
- Diesels, when well cared for, are very dependable.

Look up Richard on Dauntless.
https://dauntlessatsea.com

He's a TF member who's been back and forth across the Atlantic, all over Northern Europe, etc. in a Kadey Krogen. Single Ford Lehman diesel.

But in a GB 36 I'm not sure about the % of singles built. I believe far more were built as twins as it's a semi-displacement hull that is capable of some speed (at the price of high gph). So, you may not have many choices in a Single. Richard's KK is full displacement - and max hull speed is max hull speed for him.
- Twins offer better close quarters maneuvering although a thruster on a single could balance that out.
- single prop is usually more protected by the keel. Could be a significant consideration on that trip.

Nordhavn, Kadey Krogen, Selene and other fine trawlers are typically
Singles
Others here have more wisdom than I do... and also might take issue with my points. Or add more.
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Old 09-17-2017, 10:16 PM   #8
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Lest you think CaptStevev and I are in cahoots, I posted my reply before seeing his.
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Old 09-17-2017, 10:21 PM   #9
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The 36 twin is probably overweight and that is probably one of the reasons they are known as a wet boat.

If I was to look for a GB 36 it would be a single.
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Old 09-17-2017, 10:38 PM   #10
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We have twins in our boat. Last week returning from a 4 day trip we stopped to pump out. The starboard engine would not start. No previous indications. With the twins we were able to run to our home and then troubleshoot it at my leisure instead of sitting at the fuel dock and spending the 3 hours it took for me to find the problem. Having said that I would not turn down a really nice single, but would prefer twins for the reliability and maneuverability.
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Old 09-17-2017, 11:09 PM   #11
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Actually, Comodave sort of confirms the support for single diesels.
The starboard engine was repaired
In 3 hours. If that were a single he would have been inconvenienced for 3 hours, but not stranded. To me the positives for a single far outweigh the negatives. Unless you need to go fast. All of he big, planing Sprtfishermen have twins because they need to go fast.
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Old 09-17-2017, 11:21 PM   #12
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We boat in the Sacramento Delta, which is prone to shoaling a lot. Our single screw is well protected so if and when we touch, we aren't doing a whole lot of damage. We burn 4.3 gph with our single Cummins at 8.5 knts. Not bad for a 43ft boat. As others have said, if two engines makes you more comfortable, by all means get two. For me, being prepared with spare parts and an extra case of fuel filters allows me to sleep well at night. It really is a personal preference.
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Old 09-17-2017, 11:30 PM   #13
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I have had significant history with both twin and single engine boats and am happy to deal with either when necessary.. My power boat a custom built as I wanted it has twins. I will admit it would be a better boat with a single,but if I had it to do over again I would build with the twins. Aside from the redundancy of twins I find the maneuverability in tight spaces an important plus for me even with bow and stern thrusters a joy stick and a wireless remote I still like my twins. I don't think the pros and cons argument is significant and believe it comes down to what you want and what is available in the package you end up with.
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Old 09-17-2017, 11:35 PM   #14
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I once chartered a GB36 with a single Ford Lehman in it. My friend chartered another brand of 36 foot Trawler with twin Lehmans in it. We cruised side by side or in trail for a week. At the end of the trip, he took almost exactly twice the fuel as I did. I can't explain it. I expected he might use a little more fuel, but twice as much? Similar boats, you'd think he would run his engines at half the speed to equal my single engine. To this day I'm baffled by this.
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Old 09-17-2017, 11:39 PM   #15
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Single: Good
Twin: Good Good

Neither option is inherently bad (or bad bad).
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Old 09-17-2017, 11:52 PM   #16
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I once chartered a GB36 with a single Ford Lehman in it. My friend chartered another brand of 36 foot Trawler with twin Lehmans in it. We cruised side by side or in trail for a week. At the end of the trip, he took almost exactly twice the fuel as I did. I can't explain it. I expected he might use a little more fuel, but twice as much? Similar boats, you'd think he would run his engines at half the speed to equal my single engine. To this day I'm baffled by this.
That does sound odd. Were they the same exact engine in each boat? If so, it probably boils down to hydrodynamics and hull shape. Maybe his boat had a dirtier bottom and poorly sized/pitched props, or just didn't have as slippery a hull design.

Each 120 in our 46' boat burns .9 GPH at 1400 RPM. That pushes our stout 60,000-pound gal just over 7 knots. I believe the same engine in a smaller boat, say a 40-footer at 35,000 pounds, will burn fuel at the same rate at the same RPM. Though it may or may not do the same speed...
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Old 09-18-2017, 12:01 AM   #17
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That does sound odd. Were they the same exact engine in each boat? If so, it probably boils down to hydrodynamics and hull shape. Maybe his boat had a dirtier bottom and poorly sized/pitched props, or just didn't have as slippery a hull design.

Each 120 in our 46' boat burns .9 GPH at 1400 RPM. That pushes our stout 60,000-pound gal just over 7 knots. I believe the same engine in a smaller boat, say a 40-footer at 35,000 pounds, will burn fuel at the same rate at the same RPM. Though it may or may not do the same speed...
As I recall both bottoms were relatively clean. Hull design, I don't know, that might have been the difference. His boat was another name brand boat, I just can't remember what.
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Old 09-18-2017, 12:14 AM   #18
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Some years back I spent a lot of time trying to find a single engine GB 42. They are quite rare. I'm not sure about the availability of single GB 36. At the time i figured single would be best. Now I am less sure, and I quite like having twins in my current boat.

When I re-powered I did get a quote for converting to a larger single engine. The numbers did not stack up. My broker told me 'just as well, if you made it a single you would never be able to sell it'. Not for technical reasons, just buyer preference. Were I to buy another boat the 'single versus twin' factor would be way down the list of 'important distinctions' for a decision on which boat.

One factor not already mentioned is that a single is likely to have greater draft. That might not be an issue for the OP given his expected cruising area, but it would be a consideration for use in the tropics where shallow water abounds.

If fuel efficiency is an important consideration, then slow down as already mentioned. Even 1/2 kn will be quite noticeable. As will a clean bottom/running gear versus one with a lot of barnacles.
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Old 09-18-2017, 12:37 AM   #19
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Regarding fuel use.

I have twin Crusader 350 cid, 255 hp engines. Our Tollycraft is a planning hull.


For getting long distance fairly quickly we like to cruise on full plane at 16 to 17 knots. That speed = 1 nmpg.

For most short cruises we go a bit below hull speed [which calcs at 7.58 knots]. Loafing along at 6.5 to 7 knots using both engines we get right at 2 nmpg.

If we are really in mood to go slow... I shut one engine down and cruise at 4.5 to 5 knots for nearly 3 nmpg.

Be careful to check with trany manufacturer before letting one engine free wheel its prop if you get twins and do shut one down. Our Borg Warner Velvet Drive 70C trany are OK to freewheel.

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Old 09-18-2017, 12:43 AM   #20
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A single engine will get you there with half the engine-maintenance cost. A single-engine owner will/should be keeping up on engine maintenance. ... Most dual-engine boats were/are designed to exceed hull speed, with vastly increased fuel consumption.
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