Dink OB - Long Shaft vs Short Shaft

[44'cruisingcat]

Originally Posted by txh2oskier

Yesterday I was unable to get "Quote" to work so it may have appeared my response was aimed at you. It was not. colemj said the original poster (me) was lazy and bought the wrong dinghy or wrong outboard. He needs to go back and read my original post.

Enough said.

Ah, no. Colemj was referring to a PO - previous OWNER of his dinghy. The lazy reference was due to Terra Nova saying it would be just lazy shopping to buy a mismatched dinghy or outboard.

In my case if paying half price was lazy, then yeah call me lazy!

[colemj]

Originally Posted by a64pilot

They were also I believe 5/8 an inch low, not 5 inches. Point of the link was to illustrate proper height, it had a picture, not anything else.
The adjustable plates you refer to are called Jack plates, Last Jack plate I had was hydraulic and adjustable at the helm, you had to start out with the motor dropped or the prop would "blow out". I've been away from those high horsepower go fast boats for awhile, but I've not seen a manufacturer put a Jack plate on their boat, dealers yes. but manufacturers DO provide adjustable mounts, every motor I have ever seen has a row of holes to raise or lower the motor, and another row of holes to adjust the tilt . These adjustments do have an effect, often a substantial effect, many times allowing a smaller motor properly set up to perform satisfactorily. Often times it's the difference between planing and not. Now you don't see me advising people on how to set up their sails etc., but motors and power boats I have a little knowledge in.
Ask yourself this, if length doesn't matter, then why are they available in different lengths?

Now if you just want to putt putt around and or have to use your big boat motor for the dink for financial reasons, sure get a long shaft, just don't be surprised when a 9.9 outperforms your 15 though, cause it will.

I got almost 5 kts out of "propping" my motor and another 3 from getting it to the right height, needs to go a little higher actually, but hey it is a dink it's fast enough.

Again, your experiences with large motors on boats does not translate linearly down to small outboards. For example OB's do not need very fine height adjustments, and they do not contain mounting height holes as you describe. Tilt, yes. Height, no. Go look at your Suzuki and tell me where the height adjustment holes are. Then count yourself as now having seen an OB without those.

I have to laugh now - you bought a motor with a shaft too long for your dinghy?

Of course length matters - there are very short transom boats where even a 15" shaft is too long, but even more importantly, there are high transom boats that need a 25" shaft to get the cavitation plate to the water. Asking that question is non-sensical and has no bearing in this discussion at all.

As for transom jacks - I'm not talking about those large complicated things used on large engines. I'm talking about some aluminum plate bent to the thickness of the transom and bolted through it.

No need for SS - just use some Al channel the proper height you want and bend some 1/8" Al diamond plate around it and bolt it to the transom.

I can't find a good pic right now of our old dinghy that used a riser, but here is a pic - look closely at the transom mount and you can see the riser.

You can buy these commercially, but making them is very easy.

If you only need an inch or so, I would just put a wood or aluminum spacer on the top of the transom and clamp the engine down on it.

But there will be NO death and destruction if you leave it too long.

BTW, I used the old OB with and without that riser and had zero speed difference from the extra 3-4" without it.

Mark

[colemj]

Originally Posted by txh2oskier

Yesterday I was unable to get "Quote" to work so it may have appeared my response was aimed at you. It was not. colemj said the original poster (me) was lazy and bought the wrong dinghy or wrong outboard. He needs to go back and read my original post.

Enough said.

Sigh.

Dude, I have been SUPPORTING you this whole thread. It was two other posters who called you lazy and buying wrong stuff.

I have spent quite a few posts fighting that those statements FOR you.

Mark

[colemj]

Originally Posted by a64pilot

You don't want a long shaft on a dink

Originally Posted by Terra Nova

This.

Here you go.

Mark

[a64pilot]

I've got a piece of 304 SS pipe, I think 1.5" raising the motor now, and that is sort of Mickey Mouse and as high as I can raise it and the clamps still get a good bite on the original transom.
I've never installed the thru bolts on the motor yet, but surely there are several holes, maybe even just a couple? I don't think I have ever seen a motor with just one set, but this is my first little motor in a Long while. I've never had a 9.9,, last motor was a 10HP , it's been that long ago. It was a Quicksilver, green and silver little motor.
I was thinking install the bolts as a theft deterrent as much as anything and just deal with the extra work to remove the motor myself.
I like tinkering and I think there is still some left to be had, I think I remember 35 kts with just me and the 12" prop in a slight chop, but I am running the 11" prop as it is a better compromise of rapid acceleration and top speed. If I raise the motor till the anti cav plate is flat, I think I can run the 12 more easily.
All this is not necessary, but is fun tweaking performance out of something. Really need a tach to do it right though.


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[colemj]

Originally Posted by Terra Nova

it seems a pity that all that experience you claim to have is not tempered by a tiny bit more common sense.

Funny, I was going to say the same to you.

At least I have put forth my experience and reasoning here.

I can't say the same for you.

Mark

[Jim Cate]

Hmm...

No input re the theoretical evils of long shafts on dinks, but the old Zodiac Mk 2 that came with our previous boat had a Johnson 15 with a 5 inch extension. Inever measured the depth of the cav plate, but it was well submerged with the dink unloaded, and deeper yet with passangers, etc. Used that setup for several cruising years, hundreds of hours operation.

We never flipped, spun out, suffered from torque effects or noticed speed loss, though that was only subjective, of course. The only observable effect was that when beaching the dink we needed to tilt up a bit further from s hore than our mates with short shaft outboards.

All this sturm und drang is pretty silly IMO. There are plenty of mismatched o/b and dinghy pairs out cruising, fatalities are rare.

Jim

[a64pilot]

Originally Posted by colemj

Here you go.



Mark

I still say you don't want a long shaft on a dink, it will work depending on how you define work, but it is not optimum, unless of course a dink is made for a long shaft, just cause I've never seen one doesn't mean one doesn't exist, but I've not seen one. I can see a market maybe, that way you can use the same engine on your boat and your dink?


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[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.

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[a64pilot]

Originally Posted by colemj

Here you go.



Mark

I still say you don't want a long shaft on a dink, it will work depending on how you define work, but it is not optimum, unless of course a dink is made for a long shaft, just cause I've never seen one doesn't mean one doesn't exist, but I've not seen one. I can see a market maybe, that way you can use the same engine on your boat and your dink?


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[colemj]

Originally Posted by a64pilot

I've got a piece of 304 SS pipe, I think 1.5" raising the motor now, and that is sort of Mickey Mouse and as high as I can raise it and the clamps still get a good bite on the original transom.
I've never installed the thru bolts on the motor yet, but surely there are several holes, maybe even just a couple? I don't think I have ever seen a motor with just one set, but this is my first little motor in a Long while. I've never had a 9.9,, last motor was a 10HP , it's been that long ago. It was a Quicksilver, green and silver little motor.
I was thinking install the bolts as a theft deterrent as much as anything and just deal with the extra work to remove the motor myself.
I like tinkering and I think there is still some left to be had, I think I remember 35 kts with just me and the 12" prop in a slight chop, but I am running the 11" prop as it is a better compromise of rapid acceleration and top speed. If I raise the motor till the anti cav plate is flat, I think I can run the 12 more easily.
All this is not necessary, but is fun tweaking performance out of something. Really need a tach to do it right though.

There are two thru-bolt holes on each side that are spaced 5/8" centers from each other. These are more about having a clear spot to drill through the transom than they are height adjustments. You would not want the motor bearing all its weight and force load on two 1/4" bolts in a (relatively) weak transom layup even it they were inches apart. You always want the motor clamp resting on a transom top.

Theft deterrent is a side benefit of the thru-bolts. The real reason for those bolts is to hold your engine onto the transom. They are actually required to be installed by the manufacturer. I lost count of the number of people we know who relied only on the hand screws and lost their OB overboard when it jumped off the transom.

I bet some here warning about the dangers of an extra 5" of shaft are mounting and operating their OB's on only the hand screws.

If you are mounting the OB every time you use the dinghy, then you have a bit of safety margin here because you will be putting a fresh clamp force on it constantly. If you are not operating this way, you are playing with chance.

I have to ask another delicate question in light of this thread content: does your OB HP exceed the maximum recommended for your dinghy?

35kts is pretty much unheard of for most matched HP/dinghies.

If so, you may want to consider backing away from the safety argument here…

There is a small, inexpensive wireless tach for OB's. Someone posted it in a thread once, but I forgot what it was. It was a little sensor stuck inside the engine with a small readout to be put remotely.

Mark

[colemj]

Originally Posted by a64pilot

I still say you don't want a long shaft on a dink, it will work depending on how you define work, but it is not optimum, unless of course a dink is made for a long shaft, just cause I've never seen one doesn't mean one doesn't exist, but I've not seen one. I can see a market maybe, that way you can use the same engine on your boat and your dink?

I guess you missed the post where I stated that our current dinghy requires a 20" shaft as per manufacturer. You also must have missed the picture of our old dinghy which also required a 20" shaft (the riser was because one of the OB's on it in its life was a 23" shaft).

So a long shaft is actually optimum for many models of dinghies. A short shaft on some dinghies would be so non-optimal as to be either unusable, damaging or dangerous.

There is a reason 20" shafts are as commonly sold across all brands and models as 15" ones.

Shafts for larger boats like you are describing are longer than 20", and are not as commonly sold among brands and models.

Mark

[Terra Nova]

Originally Posted by colemj

Here you go.

Mark

The word "This" is your damning evidence?

Originally Posted by colemj

...
I bet some here warning about the dangers of an extra 5" of shaft are mounting and operating their OB's on only the hand clamps. ..

Actually those bolt holes are put in by the manufacturer, knowing some idiot would install a long shaft motor on a short shaft dinghy; the holes allow the motor to be bolted to the transom when he realizes the motor must be raised 5" and the clamps no longer touch the transom.

[colemj]

Originally Posted by Jim Cate

Hmm...

No input re the theoretical evils of long shafts on dinks, but the old Zodiac Mk 2 that came with our previous boat had a Johnson 15 with a 5 inch extension. Inever measured the depth of the cav plate, but it was well submerged with the dink unloaded, and deeper yet with passangers, etc. Used that setup for several cruising years, hundreds of hours operation.

We never flipped, spun out, suffered from torque effects or noticed speed loss, though that was only subjective, of course. The only observable effect was that when beaching the dink we needed to tilt up a bit further from s hore than our mates with short shaft outboards.

All this sturm und drang is pretty silly IMO. There are plenty of mismatched o/b and dinghy pairs out cruising, fatalities are rare.

Jim

Jim, you have stumbled onto the non-reasoning thread where statements can be made bare-faced and not backed by any logic, reasoning or actual experience. Unless you have a stiff drink in hand, you may want to quietly go back to the reasonable threads where your actual experience and sound reasoning is valued.

Mark

[colemj]

Originally Posted by Terra Nova

Actually those bolt holes are put in by the manufacturer, knowing some idiot would install a long shaft motor on a short shaft dinghy; the holes allow the motor to be bolted to the transom when he realizes the motor must be raised 5" and the clamps no longer touch the transom.

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

Is this opposite day? Are you intentionally meaning for everything you post here to be wrong? I'm trying to give you the benefit of the doubt here, because my other explanation disappoints me.

Would you like to back up your above statement with any facts, logic or reasoning?

Would you like to start by explaining how bolt holes that are 3" from the top of the transom could be used to raise an OB 5" off the transom?

Mark