Dink OB - Long Shaft vs Short Shaft

[colemj]

Originally Posted by wellin

I would get a high torque, large prop outboard made for a sailboat even if i only ever use it on a dink. The one time the wind and tide are saying "your hitting the rocks soon" you can save yourself and your boat with your own mini crowley tug. Worth the lower performance any day.

The performance on the dinghy would be much worse than "lower" - it would be so abysmal as to be unusable to get across a swimming pool with.

If "your hitting the rocks soon", there are many more valuable things you could be quickly doing other than launching a dinghy and tying it to the boat in an attempt to pull it away.

Mark

[a64pilot]

My dinks max HP is 20 and I have a 20 HP motor, but I also know that HP rating is an algorithm and may or may not be accurate. Plate HP is I don't think a law as every Bass boat on every lake in the US way exceeds plate HP.
Yes dink is fast, real fast with just me on board, I kneel in the floor when going that fast, and only do it to play with it, and I may be wrong with that 35 Kts too. I know it will run 30 with two onboard and the 11" prop.
Bike I sold last year would run 186 MPH , 300 KPH and turn I believe a sub 10 sec quarter mile, and yet I had it for a very long time and never hurt myself on it. There are times and places where going fast is safe, or relatively so.
I know the bolts are "required" states that pretty plainly in the manual, only motor I ever lost was maybe 45 yrs ago, used to be a class of hydro's based on one sheet of 8 ft plywood and a 10 HP motor, had it fall off in a turn, found it unharmed. I need to install the bolts, I know the risks.


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[colemj]

Originally Posted by a64pilot

My dinks max HP is 20 and I have a 20 HP motor, but I also know that HP rating is an algorithm and may or may not be accurate. Plate HP is I don't think a law as every Bass boat on every lake in the US way exceeds plate HP.
Yes dink is fast, real fast with just me on board, I kneel in the floor when going that fast, and only do it to play with it, and I may be wrong with that 35 Kts too. I know it will run 30 with two onboard and the 11" prop.
Bike I sold last year would run 186 MPH , 300 KPH and turn I believe a sub 10 sec quarter mile, and yet I had it for a very long time and never hurt myself on it. There are times and places where going fast is safe, or relatively so.
I know the bolts are "required" states that pretty plainly in the manual, only motor I ever lost was maybe 45 yrs ago, used to be a class of hydro's based on one sheet of 8 ft plywood and a 10 HP motor, had it fall off in a turn, found it unharmed. I need to install the bolts, I know the risks.

Plate HP is a Coast Guard rating, I believe. While it may not be a "law" (I don't know), it probably would immediately come into play should an accident occur. It may come into play if, during an inspection, the CG wanted to make some example.

Personally, I have no issue with exceeding rated HP. After all, one doesn't NEED to twist that handle thingy so far. And load and conditions play a lot here - if you will be cruising, you will want and need all the HP you can get at times. Many times. More times than people believe before they go out cruising.

If you will be putting the OB on the dink often when using it, your risk is mitigated by vigilance. The real problem with just mounting and leaving is that dinghy transoms are terribly designed things. Most only have a really cheap, thin aluminum plate on one side and a piece of thin plastic on the other. Then the transom itself is thin glass over cheap plywood.

Over time, the plastic back can compress, the aluminum plate loses its pattern or deforms, and the actual transom can depress.

In a sharp turn, the OB has tremendous force on the hand screws (much, much, much more if the shaft is 5" extra, of course), and the screws slip and jump.

Really, I lost count of the people we have met out cruising whose OB's have jumped ship in operation. I have been on two of them, and another one that I saw happening as a passenger and launched myself to the transom and caught it right as it jumped off (pulled it back into the boat, but that was a bit of a situation in itself).

Mark

[a64pilot]

Ranger boat I had I think the plate HP limit was 150. I had 250 on it and would have had maybe more but 250 was the biggest.
That was the boat I had the Jack Plate and Hotfoot on. Hotfoot was a gas pedal, idea being if you were knocked about of course foot would come off pedal and engine would go to idle, and of course the kill cord too. If they got to chine walking, you had to be careful, you could lose control and flip the boat.
Everybody exceeds plate limit with a Bass boat, you don't have a real Bass boat unless it will run 90 MPH or more. There were even some tunnel hulls coming out.


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[Terra Nova]

Originally Posted by colemj

I knew you could out-do yourself in spouting dizzyingly silly stuff...

Hey, you started it. At least I put a happy face next to my BS to identify it as BS. You simply state it as fact, and then go on to support your "facts" with unsupported and fantastic claims of superiority.

[colemj]

Originally Posted by Terra Nova

Hey, you started it. At least I put a happy face next to my BS to identify it as BS. You simply state it as fact, and then go on to support your "facts" with unsupported and fantastic claims of superiority.

I get it now. You are only here to wind things up.

I'm sure the person who needs the information understood this before I did. Hopefully he wasn't initially derailed by your dreck and chaff.

At least he has some reasoning and experience from some of us here to help him with his situation.

Mark

[44'cruisingcat]

SO, to sum up for the OP.


Ideally you'd want the shaft length on your outboard to be the one that suits your dinghy.


But if the long shaft motor is a really great buy, (and your dinghy has a short-shaft transom) it will work. Maybe you won't get every possible knot out of every HP you might have, but unless you're really anal you very likely won't notice the difference.


It will be a couple of kilo's heavier than a short shaft. It will also draw more.


It won't be dangerous.

[a64pilot]

One thing for sure a short shaft will not work where a long shaft is called for


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[colemj]

Originally Posted by 44'cruisingcat

It will be a couple of kilo's heavier than a short shaft. It will also draw more.

1 kilo difference in weight (in the case of ours it is 0.9 kilo difference). Any unwanted extra depth can be handled by a transom plate.

Originally Posted by 44'cruisingcat

It won't be dangerous.

You obviously have not been paying attention to the experienced experts.

Mark

[44'cruisingcat]

On some dinghies with transoms set up for short shaft, modifying them to suit a long shaft can be an improvement. On ours it would be for sure. (I'll get round to it one day)




Our dinghy's transom has a cut away to suit the SS. Filling this would make the dinghy less susceptible to pooping or water coming over the transom in a quick stop.

[Terra Nova]

That's one approach: buy the wrong motor, then modify the dink to fit.

[colemj]

Originally Posted by a64pilot

One thing for sure a short shaft will not work where a long shaft is called for

Mark

[44'cruisingcat]

Originally Posted by Terra Nova

That's one approach: buy the wrong motor, then modify the dink to fit.

I take it you can't/don't read posts. Just blabber your irrelevant opinions...

I already had the motor. I bought the "wrong" dinghy. If you call a brand new 3.5 metre hypalon RIB with a ton of accessories for under half price buying the wrong dinghy.

And when I modify the transom (which is easy) it will be a better dinghy than if it had a SS motor.

[Terra Nova]

Having owned several versions of the especially excellent 3.5hp Tohatsu/Nissan 2-stroke (without shift), when a pair of brand new 3.5 long shaft outboards became available, locally, a friend and I pounced on them. As you can no longer buy them in Ca. But it was just ridiculous on my 2.85 Avon roll-up. And so I passed it along to another friend. Presently have a near mint 3.5 Tohatsu short shaft (plus a Yamaha 3 and Johnson 15). The short shaft 3.5 will easily plane my dink, solo. But the long shaft would not.

One problem not yet mentioned is how a long shaft motor unmercifully twists the wooden transom on a non-rigid inflatable, due to the increased lever arm.

[Stu Jackson]

Originally Posted by colemj

Since some here have reading comprehension issues, I would also like to reiterate what I posted earlier - that the worse that could come from this is that the OP may need to install a transom riser. These are cheap and easy - it could be as easy as adding a wood batten to the top of the transom, but they do make specific risers.


Mark

Exactly what I've done, and I have a short shaft on a Zodiac air floor 10.2. It wouldn't work well without it. And sooo simple.