Twin to Single conversion- Oh My!

[JohnP]

Eric,* I think if I had a big boat I would skip the Flybridge as the pilothouse would be so commodious the whole party could enjoy the view and lounge or dine while the helmsman could bask in their company.

You get the picture.*** JohnP

 

[sunchaser]

A well laid out FB on a nice warm day is lots of fun. On ours we have:
--Seating for 8+
--All the necessary instruments
--Map table
--Full layout dayberth for snoozing
--Enclosed or open dependent upon temps
--Great 360 degree vision for spotting things
--Seaview glass window with wiper in the front for visibility in rain

 

[Nomad Willy]

And Tom,
Your boat's plenty big and wide enough to support that FB.
If you gave me your boat I wouldn't remove the FB either.
If a FB weighs next to nothing I would'nt critisize it even on
a 25' boat if was'nt too high up. I guess I've made my point
that the FB dosn't help seaworthyness but in most all conditions
the FB dosn't make the boat unsafe either. If it's fun to poke
at me about this I'll poke back untill everyone's asleep.

 

[El Sea]

If no CG issues with a FB, how about windage?

With*an Oxygen Tent (A.K.A. FB)*extending an extra 6 to 7 feet above, would that not attribute to windage?

Then wouldn't extra weight/ballast have to be placed below the CG to offset the windage?

 

[Nomad Willy]

El Sea,

Big time


Big time


Would be good but almost never done.

 

[sunchaser]

El Sea

When we dock in 20 - 25 knots the windage from the fly bridge enclosure doesn't seem an issue. But our DeFever is very deep and heavy. I've watched many lighter boats, including my previous ones,* blow around in 10 knots with no flybridge.

 

[FF]

For folks that run the AICW a fly bridge might slow your progress to sail 6K cruise speeds.

IF you need a lift on every bridge it is common for the tender to assemble a pack , rather than grant individual OPENINGS.

SO you get to mill about for a half hour as the snail sail boats gather from the last bridge opening.

While it has a great effect on interior volume (a religion for some) our 12ft bridge air height probably saves 3 or 4 days on an ICW migration.

Decide weather the oxygen tent will be a bother where you live and cruise .

 

[Egregious]

JohnP wrote:******* There were tons of twin screw trawlers built in the hay days back in the 70s and 80s.** It is possible there could be a huge glut on the market as these boats age.
The little guy $$$ is being squeezed out of boating and the big guy $$$ will want something newer than these 30+ year old boats.

******* As these boats sit on the market and deteriorate their value will plummet.

Ahh, do you know what a Monk 36 sold for in 1983?* And what one in good condition sells for today?* not including inflation, that is a pretty good deal.

Boats are wierd.* Something you don't need and can last forever if taken care of properly.* Who would buy that?

*

 

[Airstream345]

This is an old thread and one I wish I hadn't found. It's got me thinking stupid thoughts about my hollow bilge.

 

[O C Diver]

This is an old thread and one I wish I hadn't found. It's got me thinking stupid thoughts about my hollow bilge.

Thoughts aren't stupid; they stimulate the brain. Acting on these thoughts is where people start to question your sanity. Think your thoughts; take some measurements; draw some sketches; get some prices. Until you pull the trigger, there's nothing wrong with "what if....."

Ted

 

[RT Firefly]

Greetings,
Mr. A. I usually can't remember yesterday and this topic was LONG forgotten but thanks for bringing it back. I think the most viable option mentioned was put in a single and run the twin shafts via hydraulics.
One would still have the maneuverability of twins with the potential extra space and economy. That idea has always appealed to me.



I just did a quick thought about our boat and it wouldn't work. Our ER has twins (Lehman 120), 15KW generator, 4AC units, battery bank (2-4D's and 6 GC) and a stackable washer and dryer. Other than the expense, I can't see how a single could replace the twins and still allow the good layout we have now. Aw SNAP!


Still, it's not hard to run hydraulic hose so I could relocate the single engine to the guest cabin....Take out the queen bed and put in two singlebeds....Lots of sound insulation....Hmmm...

 

[johnma]

********* This is something that would be interesting-**

**********How about hydraulic motors driven off a single?

********* JohnP

*

Interesting you brought up hydraulic motors. I was involved in a few projects many years ago that used hydraulics. A naval architect contacted me about a 180' sailboat he was building that had hydraulic winches, thruster, genset and windlass and wanted to know about using a hydraulic motor for the prop. we set up a hydrostatic pump driving a low speed high torque radial piston motor for the prop. I piggybacked a load sense pump to the back of the hydrostatic pump to drive everything else. The big advantage was his ability to mount the engine in the best location for ballast rather than having it towards the back of the boat. Also because of load sensing the parasitic power losses in the entire system were very low. Was also involved in about a dozen hydraulic drives on commercial fishing boats for Chesapeake waterman. There are now large commercial ships being made with pod drives using hydraulic motors.
John

 

[Nomad Willy]

Opening a can of worms here.

******* Lets say a friend of mine (okay me)* buys a quality trawler in the 42' to 48' range.

The boat is cheap but mechanically a nightmare.* The engines are not taken care of, rusty, oily, smokey.

The engine room is a tangle of wires and hoses everything is old and on its last legs.


To make matters worse one prop is bent the shaft suspect and a rudder cracked.


Okay you get the picture the boat is a project.


********* What if I gutted the engine room and started fresh. Everything new.

**********Dump the old engines and put a brand new modern engine on centerline

********** with new drive train and centerline rudder.

********* Even redo as new the instrument panel with a single engine layout.

********* Throw in a bow thruster for good measure.


Here is the question- I know it would be a fun project and take a lot of time and $$$



But would the boat be harder or easier to sell, compared to simular twin engine models with decent engines?

Basically I am asking is the boat being ruined or improved?

Seems supply is limitless in this size for twins and very few singles can be found.

I assume the boat with one modern engine would be more economical to run and maintain.

Okay let me have it.

JohnP

John,
Forget the single engine thinking.
Decide how fast you need to go and how much power it will take. If it’s considerably slower than the capabilities of the existing boat twin 55hp Yanmar JH engines would power a GB36 to about a 7 knot cruise.

You’d retain the twin engine maneuverability with a big reduction in weight. Twin engine redundancy also. Two big features. It’s been done. I saw this combo on YW several years ago. Boat didn’t stay on YW very long either. Sure would be easier than going single too.

Just an idea and the JH Yanmar is so common you may find both engines used.

 

[Nomad Willy]

Interesting you brought up hydraulic motors. I was involved in a few projects many years ago that used hydraulics. A naval architect contacted me about a 180' sailboat he was building that had hydraulic winches, thruster, genset and windlass and wanted to know about using a hydraulic motor for the prop. we set up a hydrostatic pump driving a low speed high torque radial piston motor for the prop. I piggybacked a load sense pump to the back of the hydrostatic pump to drive everything else. The big advantage was his ability to mount the engine in the best location for ballast rather than having it towards the back of the boat. Also because of load sensing the parasitic power losses in the entire system were very low. Was also involved in about a dozen hydraulic drives on commercial fishing boats for Chesapeake waterman. There are now large commercial ships being made with pod drives using hydraulic motors.
John

Vetus markets such a system in various configurations.

 

[ksceviour]

That's.... an ambitions project. If it's been done already on that particular style of vessel then you have a proof of concept to work from however if not then it's an expensive experiment. Much simpler to drop in replacements and spend your time and money on the myriad of challenges that will undoubtedly arise from that alone. Then you could sell the boat for a profit (why is everyone laughing....it could happen) and purchase the single engine ship you seem to want.

 

[FF]

One big hassle is with Twin props and shafts they are still unprotected from debris and grounding .

I kind of love the LST tranny setup , 2 engines turning one massive shaft , either can be disconnected with the pull of a lever.

60hp for economy , 400hp to make big waves.

 

[OldDan1943]

I don't think I would take on a project of converting a twin to a single, I would just install a couple of nice little diesels sell the boat and look for a good single engine hull to do up.

Benn

I totally agree with you!!!

A couple of naturally aspirated would be perfect.

 

[FF]

"A couple of naturally aspirated would be perfect."

You bet, the turbo is usually an add on to make the engine more powerful , for a short period of time, or to help fuel economy a bit .

Sadly until one gets to ship engines where a piston is sized like a 50G drum , and way larger, our boat motors are repurposed from other industries.

Lawn equipment , taxi or farm tractor , bulldozer or OTR truck all are sources.

If the engines were built for boats , long periods of constant throttle , instead of turbos pumping more air into the engine for more power , the turbo could be installed as a PRT.

A Power Recovery Turbine is simply the exhaust portion of a turbo hooked to a gear box with a shaft to help turn the crank .

This uses the fuel to Capture more power , rather than Increase the engines power output.

Common on larger aircraft since WWII .

At 2 or 3 gph I am not sure many boat buyers would pay very much for a 10%-15% better fuel bill, but it could be done.

 

[JohnP]

Funny thing is I made a lot of noise about having a single engine trawler. Then I ended up with a twin anyway, the right boat came along at a price that made sense. Our 36 IG has Cummins 6bts. They run great at hull speed just barely above idle and sip fuel. Very quiet and I kind of love handling the boat with twins. She will top out at 13.5 in a trim tab induced sort of on plane (not really) Not sure of the fuel burn at speed because I almost never run her that way. The cost of putting two smaller engines in the boat would never be recouped. The Cummins are great engines and parts seem reasonable. Bringing my new boat back to New Jersey from Maryland resulted in my first towboat us call. I ran out of fuel with 300 gallons aboard. I stupidly had not checked the fuel valves and was only using a near empty center tank while the port and starboard tanks were full. Tow boat us is great! Very professional nice people. Engines have not missed a beat since than. Had a nice trip this Summer up the Hudson and out on the Erie Canal. Next Winter 2019 plan is to go down the ICW to Florida. It will be our first time in the "New" boat. That is quite a way off so I hope everything stays on track-you all know how life is. John and Miri

 

[Nomad Willy]

Well then John your’e stuck w the weight.
But if you’re into image weight is the most prominent element of a trawler.

 

[JohnP]

Well then John your’e stuck w the weight.
But if you’re into image weight is the most prominent element of a trawler.

Eric, You are right about the boat being heavy-- Besides the engines and genny she carries 410 gallons fuel and 200 water, 50 gallons black water. A hefty Muir Cheetah windlass on the bow lots of chain and two anchors, 2 heads and a separate shower room all tile floors, even has a 32" tv in the salon. Not sure about the image but she is a comfortable boat.

 

[FF]

"Well then John your’e stuck w the weight."


Most full displacement boats only use 3-4 HP per ton (2240lbs) so at 4 or 5 tons of goodies it would only work out to an extra 1 gallon per hour...$3.00?

 

[Mako]

"If you are considering a boat with a hollow keel that was offered as a single or twin, the conversion isn't that difficult."

I just came upon this old thread, and the comment above. Here's a photo of a Defever 49 trawler and it looks like this boat must have been available as a single.

 

[Lepke]

Even if the boat is free, I doubt you can come out for less than you could buy the same size boat with a single or twin engines.
One of the big problems with project boats is having enough income to keep the project going in a timely manner. And the boat gets older and less appealing to prospective buyers. Insurance can be an issue in an older boat. You gotta have insurance to stay at a marina.
If you do the work, you could rebuild the twins for less than buying another engine and fitting it to the hull.
I use to have a boatyard for larger boats. Mostly commercial. I saw a lot of project boats. Most never get finished and end up scrapped. I did some engine changes on some and most never went past getting the engine running.

 

[Max1]

Ha ha
A 13 year old thread brought back to life...

 

[OldDan1943]

Here’s a thought, if you want a single screw, buy a single screw boat.

 

[Lepke]

Just saw Groucho's Edsel. I'm old enough to remember when they were introduced. My dad bought a new '59 Ford station wagon. The dealer gave us a ride in an Edsel, trying to sell that instead. I thought it was about as different as a Mercury. As I remember, Ford was having trouble selling Edsels at the start. We coulda bought one for less than the Ford. Today it would be worth some money.