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Old 09-18-2017, 12:51 AM   #21
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Regarding fuel use. ...

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.

....
That's twice my fuel consumption at six knots.
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Old 09-18-2017, 07:13 AM   #22
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Just out of curiosity I looked for GB36s on Yachtworld. There were 19 in the US for sale. Of those, the majority were twins.
Perhaps more important (to me) was the master stateroom layouts. Of the single diesel versions, there were two with the double bed. The rest were built with separate single beds which just wouldn't work for us.
I never really understood why GB did that.
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Old 09-18-2017, 07:21 AM   #23
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I prefer a single for a bunch of reasons, but will never criticize anyone for favoring twins.

On my single, the main engine is considered and treated as "sacred". I'm not overly anal about maintenance on things like oil changes and filter changes, but if there is an issue that might affect reliability, it is taken care of right away. Engine also gets a good 360deg inspection often. Reliability has been fantastic. Never has engine failed to do its job.

Many of my buds with twins seem to have a much more lackadaisical approach to their engines, especially on boats with tight access. Why be anal? I've got two engines, the other will get me back.

Well, these guys have had many trip disrupting engine problems. Part of that is certainly due to simple probability (2x chances of a problem), but also due to their mentality.

I still knock on wood before a trip, though. Helps to mentally go through what the actions would be on any part of a trip should the engine fail. In most cases, it is as simple as dropping anchor and calling for a tow. Some longer passages you really are reliant on the beast. But a diesel that has been maintained AND has been running fine for a week is very reliable.
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Old 09-18-2017, 08:18 AM   #24
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Originally Posted by markpierce View Post
That's twice my fuel consumption at six knots.
Agreed... but 6 knots is nearing your top speed.

16 to 17 knots is my easy to do planing cruise speed with low 20's if desired. As is so often said. "In boat choices there's a trade off for everything"!

Distinct differences in our boat choice desires...

- You don't like flying bridges - We love em!
- You'd much rather single engine - We love twins!
- You like go slow FD hull design with round bilge, sloped tail and steadying sail to reduce roll - We love go fast FP hull design with hard chine and flat ass for less roll and some "get there" speed capability!

For a comparison: Figure how many $$ you spend annually. Then multiply that by 2 to 3 X. That's my cost if we both cruised equal hours per year [I believe your lifestyle lets you go boating more often and travel further than we do... so, our annual fuel cost the way we use our Tolly is really no problem]. Not a big bother to me for a bit added fuel cost; in that boat-performance of our Tolly is what we require for boating enjoyment. That's one of our trade offs!

Each to their own in soooo many life-"time" items.
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Old 09-18-2017, 08:31 AM   #25
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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.
I don't know about that. I take my single engine boat into water where twins fear to tread. My prop and rudder are protected by a stout skeg running under them. I've touched bottom and plowed bottoms that would have had twins in the yard for weeks. I like poking around in shallow water, that was a big reason I chose the boat I did.
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Old 09-18-2017, 09:14 AM   #26
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I don't know about that. I take my single engine boat into water where twins fear to tread. My prop and rudder are protected by a stout skeg running under them. I've touched bottom and plowed bottoms that would have had twins in the yard for weeks. I like poking around in shallow water, that was a big reason I chose the boat I did.
You are sooo correct!

One item re running twins [which we currently do] is extreme caution for shallows and/or flotsam.

I keep my eyes pealed while on bridge [where I pilot 99% of the time] and have depth sounder alarm at 3'- which means in regard to where transducer is set deep in bilge - I still have 2' under the props. I never do more than idle in waters less than 10' depth. When/if alarm goes off I immediately stop forward movement and reconnoiter for my next move. Usually reverse is in order, at least till the alarm stops.

I've seen full planing hull boats with twins that each have about a 1/2 length of hull keel with props, skegs and rudders set up similar to single screw boats whose keel's extend full length of hull. Often wondered if a set up like that could be designed and installed onto our Tolly's hull and drive train. Also wonder how much extra drag those two keels would add regarding speed loss and mpg reductions.

One thing I don't wonder is how much those two after market customized keels would cost... can we spell lots BIG Boat Buck$$

Guess I'll just leave well enough alone!
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Old 09-18-2017, 09:27 AM   #27
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This mirrors my approach and experiences.

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Originally Posted by Ski in NC View Post
I prefer a single for a bunch of reasons, but will never criticize anyone for favoring twins.



On my single, the main engine is considered and treated as "sacred". I'm not overly anal about maintenance on things like oil changes and filter changes, but if there is an issue that might affect reliability, it is taken care of right away. Engine also gets a good 360deg inspection often. Reliability has been fantastic. Never has engine failed to do its job.



Many of my buds with twins seem to have a much more lackadaisical approach to their engines, especially on boats with tight access. Why be anal? I've got two engines, the other will get me back.



Well, these guys have had many trip disrupting engine problems. Part of that is certainly due to simple probability (2x chances of a problem), but also due to their mentality.



I still knock on wood before a trip, though. Helps to mentally go through what the actions would be on any part of a trip should the engine fail. In most cases, it is as simple as dropping anchor and calling for a tow. Some longer passages you really are reliant on the beast. But a diesel that has been maintained AND has been running fine for a week is very reliable.
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Old 09-18-2017, 09:32 AM   #28
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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.
.
The reason older GBs are wet is the plumb bow and forward location of the wheelhouse. Nothing to do with the # of propellers in the water.
Those with twins are also more likely to be driven faster, increasing the amount of spray that will come aboard.

Anyone buying a plumb bow GB as their first boat should get a sea trial in choppy conditions, to see if they are OK with such a wet ride.
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Old 09-18-2017, 09:49 AM   #29
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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.
If you like the "safety measure of a second engine", it seems like you have already answered your question. I would caution though, that many engine problems are fuel related so if both engines are drawing from the same fuel tank(s), you've lost much of that safety measure. For the security you are seeking, each engine should draw from it's own fuel tank and you should fill these tanks at different fuel docks.

Many folks will say that a single well maintained engine is more reliable than two engines that are not so well maintained. They have a point.

In my personal boating, I am never very far from assistance so a single works fine for me. If you will be places where you cannot call for a tow, you might lean towards the twin system, keeping in mind what I posted above about fuel. And you should carry spare parts, filters, belts, etc. and have the tools and mechanical knowledge to make repairs as needed.
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Old 09-18-2017, 11:16 AM   #30
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The really important thing about single v/s twin is that it's much more about 120hp or 240. Single v/s twin would be about a 32GB w a single 120hp or twin 60hp. Or a 36 w twin 100hp or a single w 200hp.

A SD trawler should be designed for a range of power but not nearly doubble or half. 80 or 110hp .. 110hp or 140hp. 180 or 230 ect ect. Not 250 or 500. FD boats have even a more narrow range than that and planing hulls sometimes are double and half.

But in the case of the trawlers of the 70's and 80's many boats had too much and in a few cases too little power. So It's a question mostly of how much power and less about twins or singles.

Edit:
As I recall the original GB36 had a single 330hp 8cyl Cat. And her speed was probably 18-20 knots .. +or-. So I'm think'in her hull was probably designed for this power and speed. I refer to the GB prototype "Spray".
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Old 09-18-2017, 12:08 PM   #31
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We have owned a GB 36 single Ford Lehman for the last 25 years. The last 15 years were spent cruising Southeast Alaska. Our average fuel burn is 1.9 gph which includes the gen set and diesel heater. We generally cruise at 1700 rpm' at a speed of 7.2 knots, if we are not fighting a current, and faster if a current is in our favor. In all the years we have owned Interim we have never had any type of engine failure. I must admit that I'm very conscious about oil changes and yearly oil samples. However this year I'm removing the transmission to check for worn parts as I have 7k hours. I especially love the single screw keel protection, twins leaves your props and struts hanging in the wind.
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Old 09-18-2017, 01:00 PM   #32
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Per NW's comment, I looked online today at three 1990's era GB36's.

One had a single 210 hp Cat 3208.

One had twin Lehmans - 135 hp each (270)

One had twin Cummins- 210 hp each (420)

Quite a range...I'm not real sure I understand GB's thinking but maybe some buyers like to get up and go.

But for the OP, it would seem that you need to determine how you plan to use the boat. Because you mentioned fuel efficiency and 420 hp would seem unnecessary if you aren't concerned about planing very often.

For Gbimterim: can you hold a plane with that single, without being firewalled on the throttle?
What hp is it?
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Old 09-18-2017, 01:13 PM   #33
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I've had twins most of my life and am very biased.
I came in twice on one engine in about 50 years of boat ownership. One of those times with a partially jammed rudder from a bundle of discarded crab pot lines. Crab pot lines in general are a real problem in the PNW. Shaft line cutters help, but didn't for the bundle.
Two engines don't mean twice the costs. In my experience, about 10-20% more depending on speed and engine type. But I use engines known for reliability and zero electronic controls. With twins driving an wood, 80 ton, 83' boat I burn as little as 6 gallons an hour @ 7 knots. I usually cruise at 10 knots for 8.5 gallons an hour. These are open ocean speeds in average conditions.
Two engines give many maneuvering options. I have never used a bow thruster and never thought I needed one.
I enjoy very remote places, sometimes hundreds of miles from a port. I like the reliability best.
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Old 09-18-2017, 02:18 PM   #34
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cold water

If this inside passage is bad for floating lines, then consider the issue of clearing a single screw vs having one side fouled on a twin. Are you going down to clear the shaft, or call for help? This may determine "reliability" more than the engine(s) themselves.
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Old 09-18-2017, 08:14 PM   #35
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MANY thanks to all who weighed in on this. The pros and cons are very clear, and very useful to us as we go deeper into our search. I'm glad I posted the question and am grateful for the thoughtfulness put into answers. Let me ask, for GB 36 owners with either a single or twin: What is your gph at 7 or 8 knots? I understand there are other factors that affect this but would appreciate seeing what you have experienced.
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Old 09-18-2017, 08:29 PM   #36
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Since trap lines have been mentioned, I too recommend cutters. I have Spurs brand and I'm happy with them. In almost thirty years I've never been stopped by line. I did once find a short piece hung up on something down there so I know I've hit at least one line and probably more.

If you go for the single, have a back up plan. It could be call Sea Tow. It could be Tow with your dinghy. You could do what Murray did and mount an Outboard bracket on the swim platform.

In more than fifty years of driving single engine boats, I've only been towed in once. I didn't really need the Tow that time but I got tired of paying for Unlimited Towing and not using it. The belt broke. I had a spare. I had the tools. I had the knowledge. It was just too damn hot. I was too damn tired and my friends were sitting on the bridge drinking beer, so I called for a tow and enjoyed the ride home.
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Old 09-18-2017, 08:36 PM   #37
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There's an age old saying for cars and boats. If you're worried about its fuel consumption costs then either it's too costly over all for you... or... simply don't make use of it so much that it gives you a fuel cost headache.


You can also anchor and enjoy a boat. And, a little tow behind runabout can afford you great economical gunk holing while your "mother ship" languishes at anchor.


There's more than one way to skin a cat... err, float your boat[s]!
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Old 09-18-2017, 09:19 PM   #38
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Fuel rates vary by boat and speed

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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.
My fuel burn rates on my Ocean Alexander 456 approximated 4 gallons an hour when bringing her from Fort Lauderdale last year to Norfolk Virginia. I typically ran at 8.5 kn. My engines are twin cummins 330s.

I can tell you I think the boat would be absolutely perfect if it had only one engine. I can imagine all the extra space I would have in the engine room.

The boat before this one was a beneteau423 with a single diesel engine. We ran that often times like a Trawler and never had a problem with the engine not working when we needed it too.

I do like the maneuverability of having two screws. Combine that with the bow thruster and I can do just about anything with the boat.

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Old 09-18-2017, 09:25 PM   #39
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Were I in your shoes I would look at how I planned on using the boat for many years.


If I planned on doing a lot of long distance cruising vs doing a lot of short distances with more docking I would likely choose a single. If the opposite were planned I would likely choose a boat with twins.


We have twins. Twice in the past 5-6 years we have had to come back to the marina on one engine. There's a lot of confidence in knowing you have a second engine should one stop running.


Also, the ease in docking a twin engine boat is much greater than a single. I've driven and docked both. Singles can be learned but they're still more difficult in a wind or current than a twin.
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Old 09-18-2017, 10:54 PM   #40
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My fuel burn rates on my Ocean Alexander 456 approximated 4 gallons an hour when bringing her from Fort Lauderdale last year to Norfolk Virginia. I typically ran at 8.5 kn. My engines are twin cummins 330s.

I can tell you I think the boat would be absolutely perfect if it had only one engine. I can imagine all the extra space I would have in the engine room.

The boat before this one was a beneteau423 with a single diesel engine. We ran that often times like a Trawler and never had a problem with the engine not working when we needed it too.

I do like the maneuverability of having two screws. Combine that with the bow thruster and I can do just about anything with the boat.

Gordon
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You do mean 4 gals. per hour - per engine... for twin cummins 330s, at 8.5 kn. Right?? Or, are they using only 2 gals. per hour each???

"My fuel burn rates on my Ocean Alexander 456 approximated 4 gallons an hour"
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