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Old 11-09-2013, 04:27 PM   #1
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Powertrain choices

Hello all !


Well, after the recent demise of my boat, I have been looking at replacement options. Of course bigger and better has to be part of that

Although I am a trained and qualified mechanic its not my current career and I left it behind many years ago, but I still know my way around engines and have always done my own repairs on my boats.

Having said that I would live to get some opinions on which way to go for my next boat as I am a relative newbie to cruiser style boats.

Although the boat choice itself is a personal thing there are options regarding engines and drives.

Gents, what are your thoughts on the following, based on say a thirty foot cruiser of some kind

Petrol engine vs diesel
Twin engine vs single engine
Stern drive vs shaft

There are so many options I'd just love to hear the pros and cons !

Thanks !
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Old 11-09-2013, 05:32 PM   #2
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Twin diesels are best of course but usually best does cost more.
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Old 11-09-2013, 06:29 PM   #3
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Desiel with shaft drive. Less in the water to corrode and desiel will last longer especially with how the cooling water is used.

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Old 11-09-2013, 06:31 PM   #4
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Stern drives. Mounting the gearbox underwater "protected" against water intrusion by rubber seals. Not a good idea IMO. Seen the shell on one hauled out for a/f? Much less maintenance with shaft(s).
Definitely diesel, for safety, longevity, economy. At 30ft single is more likely to be found, your Kingston was single?.
Checked out a Cuddles 30?
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Old 11-09-2013, 07:05 PM   #5
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Bruce, yes my Kingston was a shaft drive diesel. Single engine diesels on a shaft seem to be hard to find unless your after something like what I had. Ie displacement hull and a low hp engine.

I would like to get something that gets along a bit faster as there's a places I'd like to go that a quite a trip away.

I'm thinking say a Riviera 30 type boat

I am worried about stern drives too but they seem to be on anything that gets along a bit quicker.are they really that bad ?

As mentioned above a twin diesel on shafts fits the bill but I'm concerned about the fuel cost.

Petrol engines in cruisers just doesn't seem right to me either..

Hmmm.
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Old 11-09-2013, 07:14 PM   #6
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Grantm wrote;

"As mentioned above a twin diesel on shafts fits the bill but I'm concerned about the fuel cost."

There's a difference between singles and twins but it's fly stuff and dosn't always favor one type.
But if you're talking trawlers like most have here singles are considerably more efficient just because the twins have twice the power as the singles.
But if you're talking about boats in general w the same amount of power w singles and twins the difference isn't worth talking about. For all practical purposes none exists.
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Old 11-09-2013, 07:32 PM   #7
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Grantm,
You had the best set up. Riv 30s had Volvo legs I think,you`ll get more space and speed. You might spend $ every year on leg maintenance, and they seem to attract shell.
The fuel cost for twins run at displacement speeds is not huge, but will exceed a single. What engine was in the Kingston? The Mariner 31 with twin Volvo diesels is a thought, but Volvo parts can cost. The Cuddles 30, predecessor to the Resort 35, being full displacement/easily driven usually had a small economical diesel, but was not fast.
A well defined search on a boat sales site should produce options.
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Old 11-09-2013, 08:24 PM   #8
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Greetings,
Diesel
Single
Shaft drive.
The debate regarding diesel vs. gas propulsion has been covered before on TF. Longevity, safety (explosion hazards), efficiency (?), repair/replacement costs etc.
Likewise the controversial single/twin debate. A single will give you more room in the ER for service and storage etc.
Outdrives are more complex and expensive to repair. KISS.
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Old 11-09-2013, 08:28 PM   #9
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Single diesel, shaft drive is keeping it simple. But you know, over there in OZ you've got another option I think...., I wouldn't even blink about a single or twin diesel outboards in a cruising application. With a single, I'd even add a diesel kicker on a separate bracket for the dinghy and get-home.
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Old 11-09-2013, 08:40 PM   #10
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Personally I'd only consider stern drives in saltwater if out of water storage of some sort(lift, rack, trailer) was anticipated. They do not forgive neglect well IMO.

I run a single gas shaft drive with no complaints but see the advantages twins or diesel offers. All have advantages and disadvantages depending upon your usage and circumstances. Horses for courses.
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Old 11-09-2013, 11:58 PM   #11
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Thank you all for your insight. No doubt I have stumbled across a debate that has been going on since Noah built the Arc and Jesus told him to run a single shaft drive diesel to ensure we all made it. )

Bruce the Kingston has a Perkins 4236 80 hp. Had a top speed of about 6 knots

I just found it too slow for me as I want to travel a bit.

I think my problem is that I need some speed. Ill keep looking and see how it goes.

Obviously a single diesel on a shaft is the go, if I can find the right boat.

Cheers !
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Old 11-10-2013, 02:08 AM   #12
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Quote:
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No doubt I have stumbled across a debate that has been going on since Noah built the Arc... )
Bruce the Kingston has a Perkins 4236 80 hp. Had a top speed of about 6 knots..I just found it too slow..I think my problem is that I need some speed...
On the single/twin thing, yes!
There is a Cuddles 30 in November "Afloat", 60hp Perkins, it may be too slow. My last boat was a Masters 34, single 6cyl turbo Perkins T6354, good boat, similar or lower priced than the Cuddles. Much faster than a mate`s Resort 35.
You`ll spend heaps less maintaining a shaft & gland than a leg. Happy searching.
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Old 11-10-2013, 06:32 AM   #13
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For a 30 ft rec boat nothing beats a gas engine in terms of cost , operating expenses -including maint and the size of the eventual kitty to replace it.

The problem with gas is the engines are limited to about 250 cont HP, not a problem for a displacement boat that probably needs 20-40 to cruise.

$6,000 for injectors or $18. for spark plugs , 6 Quarts of oil or 6 Gallons, cheap car antifreez VS special diesel antifreez, the list is endless .

Top of my list is SILENCE , it is far easier to quiet a gas engine than a knocking diesel.

A std single engine with a skeg big enough to protect the prop every grounding is good.

A set of line cutters is good if you plan on New England or Maine waters.

Gas engines are fairly efficient at minor loads , diesels not so good.

Here there is an 80c difference in diesel over gas so the Mile Per BUCK should work our fairlty close.
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Old 11-10-2013, 10:24 AM   #14
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Odd combination Fred.

You're the biggest supporter of Detroit Diesels and now you say silence is at the top of your list for powertrain choices. Hmmmmmm

"Gas engines are fairly efficient at minor loads , diesels not so good."

I'd wa'nna turn that one around.
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Old 11-10-2013, 11:03 AM   #15
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Odd combination Fred.

You're the biggest supporter of Detroit Diesels and now you say silence is at the top of your list for powertrain choices. Hmmmmmm

"Gas engines are fairly efficient at minor loads , diesels not so good."

I'd wa'nna turn that one around.
He's shooting straight....not what he has in his own boat.

I would go on and say diesel engines are likely quieter under way and maybe a bit noisier new idle. Gasoline engines run at higher RPMs and usually have a throatier exhaust.
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Old 11-10-2013, 11:15 AM   #16
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He's shooting straight....not what he has in his own boat.

I would go on and say diesel engines are likely quieter under way and maybe a bit noisier new idle. Gasoline engines run at higher RPMs and usually have a throatier exhaust.

In one of my rare times that I agree with Fred...

Gas is cheaper to maintain.. period.
Cheaper to rebuild or better yet replace.
Way quieter in the same boat at the same speed..
More than likely less cost per mile on a low use short haul boat..
We had a 4 cyl.8kw gas genset that was so quiet it didn't need a enclosure,it always amazed me how quiet and smooth.. absolutely no vibration.

Gas does turn boats into splinters with a little leak though...

My choice.. I just sold a 750hp twin gasser for a 275hp single diesel..
I love the noise of the motor below decks that sounds like a washing machine spinning 15lbs of metal chunks

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Old 11-10-2013, 01:44 PM   #17
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If you're planing on a significant amount of cruising at planing speeds, 20 kts or so, you cannot beat the efficiency of counter rotating, dual prop I/O. You'll most likely save enough in fuel costs to pay the additional upkeep and still have some change left over.

A diesel with I/O will save even more fuel and tends to start every time.

Twins are a benefit if you plan on a lot of docking and or maneuvering in tight spaces. Plus , you have a take home engine should one quit.

If you 're shopping new , then you can have twin I/Os with joystick docking, gas or diesel.

If you're not planning on significant hours going fast but plan on displacement speeds for most of your cruising, then a single slant shaft diesel is your best bet.

Gas , in my opinion, is for day boating.
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Old 11-10-2013, 03:36 PM   #18
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But w a diesel IO if the engines are bigger than sailboat engines there will likely be too much weight aft. Some boat designs are made/designed to carry lots of weight aft but most are not.

A straight shaft puts the weight where it should be.
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Old 11-10-2013, 06:40 PM   #19
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There is no "should" in engine placement. Most designers allow for the weight of the motors where they want them. This can be midship for typical slant shafts or further aft for pods and v drives or up against the transom for I/Os.

Of course, if one is repowering an existing boat, most likely the new motors need to be close to where the originals were.

So, if the hull is designed for the weight of motors in the stern, then most likely diesels can be placed there, too. Just so long as their weight doesn't exceed the motors being replaced.

I grew up crying on a 53' Huckins with a pair of v drive 671s in the stern. That boat floated right on her lines. All the Island Pilots we built had diesels in the stern with either I/Os or pods. They also sit on their lines.
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Old 11-10-2013, 08:45 PM   #20
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repowering is a fun thing...but when changing the equipment...obviously weight is a consideration as to how the boat was designed and for what weight...

while not rocket science...you need to do some thinking, ckecking, and ignoring....
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