4 stroke or 2 stroke?

[Richardw]

After 10 happy years with my 47 foot Trader, I thought it might be time to move up (much against my wife's idea) to a 57 foot President. My main question involves the engines. The Trader has a pair of CAT 3208T's and the President, Detroit Diesel 650hp 2 stroke engines.
I understand the technical differences between 4 stroke and 2 stroke but has anyone any ideas what the advantages might be, one over the other?
It seems that almost all boats of this size are equipped with 4 stroke units. Am I looking for a snag that doesn't exist?
Many thanks for any views.

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[Deleted User YDKXO]

Welcome to the madhouse, Richard. Just for your info, there's a little spat going on this forum in which various kiddies are throwing their toys out of the playpen but dont let that stop you asking sensible boatie questions
For a treatise on 4 stroke v 2 stroke diesels, take a look at this website

http://www.yachtsurvey.com/comparing_diesel_types.htm

Sorry cant do the link bit so you'll have to copy 'n paste it

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[longjohnsilver]

Also try a search of this site, the same question came up a few months ago and from memory I think Kim (Hollamby) gave an explanation of the pros and cons. Now found it.

...since parent merger. There will eventually be DD engines badged MTU in next year or so for leisure industry (and some MTUs badged DD in other industries.

The DD two-strokes hit great popularity for a fairly short while in the late 1980s/early 1990s as manufacturers started to look for higher horsepowers and low weight in a small package. The DD 550 was especially popular, from memory and DDEC was one of the first leisure marin electronic management systems out there.

Two main downsides are indeed noise -- and fuel economy. Some boatowners got quite badly caught out in the early days of these engines appearing because they expected four-stroke diesel consumption and got, I believe, quite a bit worse than that.

I've not got any fuel data to hand right now but would certainly be a little cautious with any two-stroke diesel boat regarding safe range until a couple of runs to check.




<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by longjohnsilver on 15/04/2003 21:54 (server time).</FONT></P>

 

[Richardw]

Am I glad to receive this info Mike! Many thanks.

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[Richardw]

Many thanks for your response Longjohn. All this help is much appreciated.

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[Heckler]

yes but the howl as you

put the pedal to the metal, along with that belch of unburnt diesel as she shoulders the load, detroit diesels for me every time, must be something to do with being a motor biker, lurv the sound of exhausts
s

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[jfm]

thermal efficiency of 2 stroke diesels

Yes would be worth checking fuel economy - I was surprised to hear that DD's are worse than 4 strokes. Presumably you can get data on www. Reason I was surprised is that massive ships often use 2 stroke diesels. These have blocks the size of apartment buildings, top out at 500rpm, and have just one enormous exhaust valve per pot at the top. Thing is, aside from high altitude low bypass ratio aero jets, these 2 stroke diesels are just about the most efficient prime movers that mankind has ever created. They convert something like 80%++ of the calorific value of the fuel into kinetic energy. (Jets are well into the 90s, btw).

This is a bit irrelevant I know. Just thort I'd throw it in

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[Blue_Blazes]

Before she sank, my boat had a Detroit Two Stroke in her.Reliable and strong, you could thrash the guts out of it all day long. Bit thirsty. Biggest downside was the impossibility of conversation under way. Noisy is not a loud enough word.

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