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Ghost
08-22-2010, 04:02 PM
I've been thinking about this a lot the last year or two. Seen some here and there discussion of the subject on the site recently, so I am trying to pull it together in one spot.

For context, I'm thinking about the 24-28 foot size range, although maybe that should be moved up to as much as 35 feet?

A few things are obvious. Redundancy of twins is an advantage in getting home when something goes wrong. Singles should be lighter and have less drag with less running gear. Also, singles have lower centers of gravity, are more efficient I think (thust/gallon), and are physically easier to work on because of the space in the engine compartment.

By and large, singles are more likely to be higher-performance engines that will be more costly to maintain. (By this I mean more costly to maintain than ONE of the twins. It gets interesting when you try to sort out the maintenance costs of two smaller, lower-performance motors and their drives versus one larger, higher performance engine.)

I'm particularly interested in specific experiences. If a boat handled badly, what was the ill behavior? Etc, etc.

HOWARD O
08-22-2010, 07:18 PM
I think when you get up to a certain size, in my mind past 30', I'd want twins. With the larger size, a cramped engine compartment would certainly be less of a concern. In a larger boat like that, you'd be more apt to be "offshore" or further away from any assistance and nice to have a get home engine. Maybe the biggest advantage of twins in something larger is simply the handling at the dock. I really wonder, once you are past 28 or 30 feet, if a single is going to be more efficient than twins.

I think past 28', I'd have to go twins. Unless it's not a performance boat of course, then a nice, single diesel with a bow thruster would be good.

DonziJon
08-22-2010, 07:29 PM
This conversation has been going on for decades...in the Aviation community.
Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? :nilly: DJ

gcarter
08-22-2010, 08:42 PM
This conversation has been going on for decades...in the Aviation community.
Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? :nilly: DJ

I remember reading that the odds of losing an engine on a twin aircraft is much higher than losing an engine on a single.

On the other hand, way back when my BIL and I owned a twin screw 30+' FBSF, I would get really frustrated when a single screw 35' commercial fishing boat powered by a 600 HP Yanmar would fly by us going nearly 40.

joseph m. hahnl
08-22-2010, 09:08 PM
This conversation has been going on for decades...in the Aviation community.
Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? :nilly: DJ

1964 Trojan 31 twin inboard 225 Chrysler Crusaders, We hit a unmarked rock coming from hyannis (http://www.google.com/search?hl=en&rlz=1I7GPCK_enUS370&&sa=X&ei=CslxTNiuCsL48AbppLiBDQ&ved=0CBsQvwUoAQ&q=hyannis&spell=1). going to cotuit (http://www.google.com/search?hl=en&rlz=1I7GPCK_enUS370&&sa=X&ei=VclxTO6ODMO78gbvqMz_Cw&ved=0CC0QBSgA&q=cotuit&spell=1) Mass,cleaned the prop rudder and shaft on the port engine. starboard engine got us home

Morgan's Cloud
08-22-2010, 09:24 PM
I remember reading that the odds of losing an engine on a twin aircraft is much higher than losing an engine on a single.

On the other hand, way back when my BIL and I owned a twin screw 30+' FBSF, I would get really frustrated when a single screw 35' commercial fishing boat powered by a 600 HP Yanmar would fly by us going nearly 40.

And to add insult , he'd handle the boat around the dock like he had twins AND a bow thruster on every corner ... :kingme:

Sweet Cheekz
08-22-2010, 10:51 PM
Seems this is a constant question with 27 magnum guys. I am going twins for rough water safety getting home in the event of a engine failure. Conquistador went big fast single. I think it depends on how you boat
Parnell

The Hedgehog
08-23-2010, 02:52 AM
Kind of apples vs oranges. To around 70 mph, a single is a cheaper. Above that it is close. Twins in a smaller boat can be a pita to work on, but I don't hear much grumbling from the 28ZX twin guys so it must not be too bad.

Twins are better if you boat long open stretches of water due to the get home factor. I like them both in their own way. I love the speed my big single has and it is nice to climb into the engine compartment. I boat mostly on lakes.

The Hedgehog
08-23-2010, 02:59 AM
I remember reading that the odds of losing an engine on a twin aircraft is much higher than losing an engine on a single.

On the other hand, way back when my BIL and I owned a twin screw 30+' FBSF, I would get really frustrated when a single screw 35' commercial fishing boat powered by a 600 HP Yanmar would fly by us going nearly 40.

I have not heard that stat but I can see that as most twins are complex aircraft (ie constant speed prop, landing gears etc). I do know that if you lose an engine at speeds below VMc (Velocity of minimum control) it is very bad. You have one engine running WFO and the other windmilling. This causes a bad inverted spin that makes for a smoldering black spot on the ground. Many failures seem to occur around that speed as you are squeezing the power and it is just leaving the ground. Much of the multi engine rating deals with that subject. I actually lost an engine on my multi check ride. It was a bad fuel pump. The first step is to turn on the boost pumps. Problem solved.

Conquistador_del_mar
08-23-2010, 03:12 AM
So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? :nilly: DJ

I lost one of the 302s in a twin engine 25' Wellcraft Nova once - no problem getting back, in fact it actually got on plane - barely, though. I lifted the drive on the broke engine as much as possible to help reduce drag. Looking back, I could make the case that it might have had less drag by leaving the drive down with the cavitation plate being parallel to the water flow. Does anyone know which way would be less drag? Bill

Conquistador_del_mar
08-23-2010, 03:18 AM
Seems this is a constant question with 27 magnum guys. I am going twins for rough water safety getting home in the event of a engine failure. Conquistador went big fast single. I think it depends on how you boat
Parnell

Yep, if I boated the ocean or went on extremely long cruises I would go twins. I personally think somewhere around 28'-30'+ deep v hulls almost necessitates twins. Bill

gcarter
08-23-2010, 07:18 AM
This discussion could get into a Diesel vs. gas too, since Diesels are so dependable.
It's easy to imagine a 500-700 HP single Diesel in a 30' performance boat.
Think about having 75%-80% of 700 HP available all the time instead of just once in awhile.
This would be Carl's dream boat! :)

I remember in the early days of deep-vee offshore racing, Diesels were popular. They still are in Europe, I guess.
I think it could be a financially workable situation too if you considered the cost of a single Diesel vs. the cost of two built gas engines.

Craig S
08-23-2010, 12:15 PM
Yea, but what about all those extra guages...and the extra exhausts when pulling up to the favorite eatery?

And don't forget the syncopation of the stainless trumpets for the crowds.

Ghost
08-23-2010, 08:19 PM
This discussion could get into a Diesel vs. gas too, since Diesels are so dependable.
It's easy to imagine a 500-700 HP single Diesel in a 30' performance boat.
Think about having 75%-80% of 700 HP available all the time instead of just once in awhile.
This would be Carl's dream boat! :)

I remember in the early days of deep-vee offshore racing, Diesels were popular. They still are in Europe, I guess.
I think it could be a financially workable situation too if you considered the cost of a single Diesel vs. the cost of two built gas engines.

I love the idea and actually thought a lot about doing exactly that. Except, even a Konrad isn't rated for that kinda torque. What sort of drive would you use with it? Gearbox to split it and run two drives (like Dorado Marine)?

Ghost
08-23-2010, 08:24 PM
I lost one of the 302s in a twin engine 25' Wellcraft Nova once - no problem getting back, in fact it actually got on plane - barely, though. I lifted the drive on the broke engine as much as possible to help reduce drag. Looking back, I could make the case that it might have had less drag by leaving the drive down with the cavitation plate being parallel to the water flow. Does anyone know which way would be less drag? Bill

I'm thinking you did it right, unless you were running really slowly and the water was rising very quickly behind the boat. If you did leave it down and in neutral, might not be too bad either.

Can I ask about your Nova? (HP, performance)? How'd you like it? What would you change?

gcarter
08-23-2010, 09:06 PM
I love the idea and actually thought a lot about doing exactly that. Except, even a Konrad isn't rated for that kinda torque. What sort of drive would you use with it? Gearbox to split it and run two drives (like Dorado Marine)?

There's gotta be some used #6's somewhere.
A racing engine (like the new 1300) would have similar torque, don't you think?

G-MAN
08-23-2010, 09:25 PM
This conversation has been going on for decades...in the Aviation community.
Pretty indisputable in aviation: Lose an engine (with twins) and the remaining engine will get you to the Crash site.

So has any one on this forum lost an engine...and been able to Steer the boat well enough to get home..? :nilly: DJ
Yes It would not run on plane with one motor but the one motor got us the 25 miles back home.
and yes you can still steer the boat

G-MAN
08-23-2010, 09:33 PM
I lost one of the 302s in a twin engine 25' Wellcraft Nova once - no problem getting back, in fact it actually got on plane - barely, though. I lifted the drive on the broke engine as much as possible to help reduce drag. Looking back, I could make the case that it might have had less drag by leaving the drive down with the cavitation plate being parallel to the water flow. Does anyone know which way would be less drag? Bill
Been thinking that if a guy carried a low pitch prop for me that might be like a 22p 4 blade that if you could change it in the water ( i've done that before ) that you might be able to get on plane be it a slow speed.

G-MAN
08-23-2010, 09:36 PM
Kind of apples vs oranges. To around 70 mph, a single is a cheaper. Above that it is close. Twins in a smaller boat can be a pita to work on, but I don't hear much grumbling from the 28ZX twin guys so it must not be too bad.

Twins are better if you boat long open stretches of water due to the get home factor. I like them both in their own way. I love the speed my big single has and it is nice to climb into the engine compartment. I boat mostly on lakes.
My 35 is better to work on than my 28 but not much better
on a side note we are looking for a single engine go fast to save time on the 35 and save gas$

Ghost
08-23-2010, 09:54 PM
There's gotta be some used #6's somewhere.
A racing engine (like the new 1300) would have similar torque, don't you think?


Uh oh. More ignorance on my part--I dunno what a #6 is...

gcarter
08-23-2010, 10:02 PM
Uh oh. More ignorance on my part--I dunno what a #6 is...

A Mercruiser racing outdrive.

8318
08-24-2010, 08:14 AM
I have a 32 Sutphen wit a single 540 in it and love it.the boat runs just shy of 80 78.6 last year at 5 grand this year after a motor refresh over the winter we are getting 5300 out of it. the gps is dead this year so not sure of speed but it is better than last year.
The boat is a dream to work on plenty of room. In the chop it is competitive with way faster boats due to the wonderfull balance when the boat is out of the water. the other nice thing is the fuel milage is outstanding! last week we ran the Fall River Poker Run boat was full of gas the run was around 60-70 miles. The next day we took the boat from Falmouth to MV only 6-7 miles but then crusied around in the bay and back home up the river, we must have covered 15-20 miles. I filled the boat up when we got home it took 64 gal to fill it up.
Outdrives are an issue when running this sort hp the guy that owned the boat before me went through 2 drives a summer for the past 2 years. I got the boat and put an Imco Xtreme Advantage SC drive with a Imco 2" shorty on the boat last year and have not had any issues with this drive.

I love my single
Dave

The Hedgehog
08-24-2010, 10:11 AM
I have a 32 Sutphen wit a single 540 in it and love it.the boat runs just shy of 80 78.6 last year at 5 grand this year after a motor refresh over the winter we are getting 5300 out of it. the gps is dead this year so not sure of speed but it is better than last year.
The boat is a dream to work on plenty of room. In the chop it is competitive with way faster boats due to the wonderfull balance when the boat is out of the water. the other nice thing is the fuel milage is outstanding! last week we ran the Fall River Poker Run boat was full of gas the run was around 60-70 miles. The next day we took the boat from Falmouth to MV only 6-7 miles but then crusied around in the bay and back home up the river, we must have covered 15-20 miles. I filled the boat up when we got home it took 64 gal to fill it up.
Outdrives are an issue when running this sort hp the guy that owned the boat before me went through 2 drives a summer for the past 2 years. I got the boat and put an Imco Xtreme Advantage SC drive with a Imco 2" shorty on the boat last year and have not had any issues with this drive.

I love my single
Dave

Neat looking boat. Very cool.

8318
08-24-2010, 10:32 AM
Neat looking boat. Very cool.
Thank you I love my little Donzi but my Suthpen is my true love (boat that is)

realbold
08-24-2010, 03:56 PM
80 mph in a 32 sutphen with a single is awesome.

Mike, I bet your Nova would be faster with a single 502 I/O. It might draft deeper though.

blackhawk
08-24-2010, 04:24 PM
There's gotta be some used #6's somewhere.
A racing engine (like the new 1300) would have similar torque, don't you think?

It would be close depending the rpm a Diesel runs. I'm guessing they're about 3000 rpm??? If so a 700hp Diesel would still have more torque by a couple hundred pounds.

Propping 700 hp at that low of rpm would be the next challenge. :nilly:

handfulz28
08-24-2010, 04:49 PM
RE: Diesels
2-speed trans and an ASD.
Done.
:D

NJFASTECH
08-24-2010, 06:05 PM
It would be close depending the rpm a Diesel runs. I'm guessing they're about 3000 rpm??? If so a 700hp Diesel would still have more torque by a couple hundred pounds.

Propping 700 hp at that low of rpm would be the next challenge. :nilly:

Is that avatar ac in the background or point ? Did you run that Pantera?

NJFASTECH
08-24-2010, 06:09 PM
80 mph in a 32 sutphen with a single is awesome.

Mike, I bet your Nova would be faster with a single 502 I/O. It might draft deeper though.

My 01 Fountain with the single 500 efi would run well into the 80's near 90 if you let it go and had the room.

blackhawk
08-24-2010, 06:10 PM
Is that avatar ac in the background or point ? Did you run that Pantera?

I can't remember what's in the background. It's not my Pantera, it's Scotty B's old Pantera 24.

NJFASTECH
08-24-2010, 06:10 PM
Is that avatar ac in the background or point ? Did you run that Pantera?

Kean U right?

blackhawk
08-24-2010, 06:11 PM
Kean U right?
Yep! Sure was.

Ghost
08-24-2010, 06:45 PM
Mike, I bet your Nova would be faster with a single 502 I/O. It might draft deeper though.

I'm right there with you. Been pondering it. Not sure I could bring myself to convert a Brownie Nova Marine to a single sterndrive, though my boat is pretty resto-modded anyhow.

How much lower would the motor sit? Maybe 6 inches lower in the boat? I think the 800 lbs of weight savings would have the boat sit about 4-6 inches higher in the water, compensating for most of it. (Take a look how high this single Wellcraft Nova sits, in the pic below.)

I'm contemplating (if I'm dumb enough to blow my savings on it) looking into what it would cost to build a pair of 500lb 300HP smallblocks. Maybe could end up saving about 600 lbs, keep twins, have a lot of HP and not tune the engines too out-of-sight.

I'm such a fool. Sounds fun though...


http://www.seabuddy.net/photos/d/12086-1/9+zz.jpg

realbold
08-24-2010, 07:41 PM
Those early Wellcraft Novas with single 454s were rare, I only noticed one in my lifetime. My Nova 210 with a SBC (same hull chopped off) would bottom out where everyone else in much bigger boats had no problem thanks to the steep deadrise. I'm raising the X 1" plus with a Bravo.

NJFASTECH
08-24-2010, 07:43 PM
Yep! Sure was.
I ran some of these races in my Corsa Point was the first Ha out front rookie 3/4 laps up spun a belt on the 496 HO and a long tow Home LOL.
$hit happens went on to run an F1 fountain in 5 class. My Corsa still runnig 6 class Smith bros are rocking it! Man I miss that boat!

Jim

NJFASTECH
08-24-2010, 07:49 PM
Those early Wellcraft Novas with single 454s were rare, I only noticed one in my lifetime. My Nova 210 with a SBC (same hull chopped off) would bottom out where everyone else in much bigger boats had no problem thanks to the steep deadrise. I'm raising the X 1" plus with a Bravo.

There was one with the single BB not too long ago here in the NE for sale caught my attention but not positined to purchase it. I will post them up if I see them.

Ghost
08-24-2010, 08:31 PM
There was one with the single BB not too long ago here in the NE for sale caught my attention but not positined to purchase it. I will post them up if I see them.

I think one sold on Craigslist in Detroit this past winter for $3500, with trailer. Green one I think.

realbold
08-24-2010, 09:59 PM
I think one sold on Craigslist in Detroit this past winter for $3500, with trailer. Green one I think.
I posted that ad on another board, but I thought it was a small block. Underpowered and not many like that either unless you're counting the so-called offshore models. It's no wonder they didn't sell many of those.

The Hedgehog
08-24-2010, 11:38 PM
My 35 is better to work on than my 28 but not much better
on a side note we are looking for a single engine go fast to save time on the 35 and save gas$

How fast do ya want to go?

Love the 35's BTW

smidgen too
08-25-2010, 01:01 AM
I posted that ad on another board, but I thought it was a small block. Underpowered and not many like that either unless you're counting the so-called offshore models. It's no wonder they didn't sell many of those.
It was a donated boat with a single small block OMC stringer drive.....:boggled:

Ghost
08-25-2010, 07:54 AM
I posted that ad on another board, but I thought it was a small block. Underpowered and not many like that either unless you're counting the so-called offshore models. It's no wonder they didn't sell many of those.


It was a donated boat with a single small block OMC stringer drive.....:boggled:

Interesting. I was peering at it as a pure repower job, with the benefit of no center-stringer layup and with one hole in the right part of the transom, rather than two in the wrong. Of course, I never got so far as to look into x-dimension and other stuff, just figured it was a much easier path than converting a twin boat.

zelatore
08-25-2010, 01:58 PM
One point of interest, a certain diesel engine manufacturer is about to release a new V8 diesel that's supposed to weigh in less than an 8.1 Merc and fits in almost the same size envelope. Should be in the 300-500 hp range.

And they're going to offer a stern drive with it.

I think the official debut will be Miami, but rumor is they'll have one in a boat at Lauderdale, just not on the stand.

I'm sure Buiz knows all about this, myself I only know a little.

Oh, btw, most modern turbo diesels are turning closer to 4000 rpm; at least in the smaller 300-500 hp range. The big boys are still running lower revs.