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Old 25-08-2010, 20:17   #1
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Two Stroke vs Four Stroke

My 15hp 2 stroke outboard has died for my rib 310. When talking with some people they claim that the 4 stoke does not have the immediate power of a 2 stroke engine. My old evinrude weighed 77 poiunds vs new 15's weighing more than 100. Any advice on an outboard that can get a AVon Rib310 up on plane with 4 adults and still weigh little enough to carry down the transom ladder by a 62 year old sailor. I am avoiding using the davits since the avon slides down the transom and the outboard would not.
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Old 25-08-2010, 21:24   #2
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I currently have a mid eightys 15 hp Johnson 2 stroke on my nine foot Caribe. You are correct about the lack of throttle response and mid-range power of 4 stroke. And as for the weight issue, it is easy to see with the spec sheets.
As for the HP rating, the maximum rated size should be on the transom of the boat. I suspect though that you whould have to go above that to get the performance you are looking for. Food for thought.......there is a reason that the boats are rated the war they are.
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Old 25-08-2010, 22:01   #3
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I'll light the fuse.....

There are resaons why 2 stroke has been a popular choice for outboards for so long. You have touched on them.

The initiation for change has been enviromental, encouraged by legislation. Advance in both technologies sparked by all of it have been great.

One funny thing is that since 2 + 2 = 4, some people thing a four stroke is twice as good as a 2 stroke. Don't laugh.
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Old 26-08-2010, 05:33   #4
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I am aware of maximum hp which is 25 but I am more interested in weight in that when I was cruising full time I was 39. NOw that I am 62 77 pounds is heavy enough to cary down transom ladder. Most 20HP 4 strokes are between 101-114lbs.
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Old 26-08-2010, 05:48   #5
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There is no doubot about initial throttle response, but unless you tow skiers thats not an issue. Low and mid range torque is very good in 4 strokes, So they tend to push you up onto the plane easier when the boat is loaded ( or overloaded).

They are a bit heavier, but trawl through the manufacturers specs, some brands are closer then others.

Coupled with significantly less fuel usage and they are much quieter. ALso the lack of needing mixed fuel ( or autolube systems).

If weight os the overriding factor, though then it will be a 2 stroke.

Dave
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Old 26-08-2010, 05:55   #6
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The Tohatsu 9.9 4 stroke (same as Mercury, Nissan) is about 80 lb and will get the boat up if the weight is distributed. Granted a bit slower but under 100 lbs. Suzuki and Yamaha make light engines also. What you would like does not exist anymore. What happened to the 15? They are normally indestructable.

Run any 2 stroke in a trash can of water and you will soon see why they need to go.
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Old 26-08-2010, 05:55   #7
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Old 26-08-2010, 06:26   #8
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I'm in the smaller is better camp..

Avon currently recommends their 310 Rib use a maximum hp of 10 and a motor weight of 88 lbs. ?

I have a 4 hp merc 4 stroke that weighs 55 lbs and it's a pain in the A@@ getting it on and off by myself.. I couldn't imagine hauling a 100 lb motor up and down a ladder to an inflatable by hand.

I wish I had gone even smaller. My 2 cents..
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Old 26-08-2010, 08:11   #9
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I read in one of the cruising rags that it is easier to find people that can work on 2 stroke than a 4 stroke when cruising in other countries, and also easier to do repairs yourself on a 2 stroke. For this reason a 2 stroke is preferred while cruising.

Don't know if that is a factor for you.
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Old 26-08-2010, 10:06   #10
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It's a matter of taste, I guess, and there is a great deal of information in the archives.

Both types have various pros and cons, but personally I just love two strokes for this application. They are indeed more responsive than four strokes and to my hand just feel better. I like they way they sound and even the way they smell. Perhaps it is a Pavlov's Dog type psychological association between two stroke smoke and freedom and happiness -- I was first taken on boats as an infant, boats with two stroke outboards.

Two strokes are lighter and they are simpler, which makes them simpler and cheaper to maintain and repair. These are very good things for this application. Their main downside is greater fuel consumption, which means less range and more fuel expense.

The bigger the engine, the greater the advantages of a four stroke. But it is hard for me to see anything good about small four strokes. From about 10 horsepower and smaller, four stroke outboards may be splash lubricated and really cheaply made, and so may be actually less durable than comparable size four stroke.

I have a 25 horsepower two-stroke Mariner on my dinghy, the latest in a long line of two stroke dinghy engines. I love it to bits. It is ten years old, but runs like a top, starts perfectly all the time, and I've never had a bit of trouble with it. It's powerful and smooth and just feels good -- it feels like it is happy at its work. It does drink fuel, however, but that is a small price to pay for the motor's other virtues, in my opinion.

I have a 40 horsepower Mercury four stroke on my lake boat. This is also a good engine, and is particularly good for low speed puttering, which is what we mostly do with that boat. It is very economical and quiet. It is heavy, but that is not a problem in that application. But for a dinghy, I would never have anything but a two stroke.
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Old 26-08-2010, 10:18   #11
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Quote:
Originally Posted by Tempest245 View Post
I'm in the smaller is better camp..

Avon currently recommends their 310 Rib use a maximum hp of 10 and a motor weight of 88 lbs. ?

I have a 4 hp merc 4 stroke that weighs 55 lbs and it's a pain in the A@@ getting it on and off by myself.. I couldn't imagine hauling a 100 lb motor up and down a ladder to an inflatable by hand.

I wish I had gone even smaller. My 2 cents..
This is an important point.

If all you do with your dinghy is go back and forth from shore a few hundred meters at a time, then the smaller the better, as long as you at least have enough power to push your way through wind and seas if necessary.

Taking that idea a bit further, some people forgo the motor altogether and just row. I know a number of people who really swear by this approach. A few minutes of pleasant rowing is much better than all the wrestling with the motor, worrying about fuel, etc., etc., they say.

On the other hand, some people use their dinghies for longer trips. That would be us. We like to use the dinghy to explore and to range far and wide. We have taken all day trips in our dinghy, up rivers, all around big bays and harbors, that sort of thing. So here the power to get the dink on a plane with four or five people on board is really important. Also console steering is really important if you are going to spend hours at a time in the dink.
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Old 26-08-2010, 10:41   #12
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Welcome to the beat-a-dead-horse Club. There are still a few good old points to be bemoaned, such as "you can still get two stroke engines in foreign contries" and several reditions of "Thank your stars you aren't getting all the government you pay for!"

I'm waiting for some truly novel reason to debate two-stroke versus four stroke dinghy engines. The fact remains that two strokes (without exotic fuel management tricks) are just not available in the US and other ecologically aware countries.

As it is, these posters seem to just enjoy repeating the same complaints, with no chance whatsoever of a reversal.

I wonder if the BP blowout has left as much polution in the word's water as two-stroke engines?
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Old 26-08-2010, 10:45   #13
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Lets assume a 2 stroke and a 4 stroke have the same amount of power output per cycle, a 2 stroke will therefor have double the power output for a same-sized 4 stroke hence the 4 stroke has to be bigger (heavier) to output the same horsepower. Add in the fact that a 4 stroke requires even more weight to function courtesy of the oil sump and valve train and you end up with the 2-stroke coming out ahead in the weight/power race with the previously mentioned drawbacks. One thing not mentioned is if a 2 stroke gets swamped (sinks) it can be successfully revived 9 times out of 10 if the submersion is brief, happens all the time with standup jet skiis (I do not have first hand experience)
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Old 26-08-2010, 10:56   #14
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Ummmmm...........why not just sail down to the bahamas and buy a two stroke? like one of the yamaha enduro engines?
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Old 26-08-2010, 11:02   #15
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or get a sailing RIB!
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