Best small petrol 4 stroke 3 or 4 h.p dingy outboard motors

[mvweebles]

Originally Posted by Celestialsailor

Where did you store the OC?


Another tender I had but was heavy to store(for me) was the Livingston 8' super dry and planed with a 6hp.

I have a Wm Garden designed trawler with a boat deck to stow tender. The pic below is a sistership, but you get the idea. Although she carries 6000 lbs ballast, weight remains an issue so a reasonably lightweight dinghy is needed. There are many dinghies such as the Livingston that are decent designs but pretty darn heavy.

I think the concept that is missing is dinghies that plane with low hp propulsion do so because they are flat bottomed. It doesn't take much to get a picnic table to plane. But if you want to run through chop, you need a deeper vee approach which will take some hp to get on plane. If your cruising is protected waters, a flat bottomed boat with small hp motor is ideal. If your cruising is more adventure oriented, a small flat bottomed dink with low hp OB will limit your options. I was at Ft Jefferson (Dry Tortugas national park near Key West). Loggerhead Key is a couple miles away, but open water with sone chop. For the few days i was there, no way I'd make that run in a PB and 3.3 hp OP.

The second attached picture are chocks I just built for my AB 310 Aluminum RIB (GPO3 stock before painting). Notice how deep the forefoot is - this RIB is rated at max 20 hp OB, which is in the range of what it takes to get this boat on-plane due to the deep vee hull form. The boat is designed to run through 2-3 foot chop. No way a PB or flat bottomed boat will do that.

[sailhand]

The 3.5 tohatsu four stroke with upgraded 5hp carb solves the annoying flatspot in the standard carb.

[MicHughV]

Hull shape is everything.

My first ever dink was a fiberglass rowing dink, probably around 9-10' in length. A 2 hp OB pushed it along just fine.

In a drunken inspired moment, I convinced some other sailors to allow me to strap their engines to the transom of that dink in addition to mine.

The result was that I went nowhere fast. The dink was not going to plane, even if I strapped 100 hp to it. Instead, best I could manage was bow standing up at 60 degrees, with the transom an inch above the water.

Thus ended that experiment.

[Dockhead]

Originally Posted by sailhand

The 3.5 tohatsu four stroke with upgraded 5hp carb solves the annoying flatspot in the standard carb.

That's interesting!

But wouldn't that be overcarbed with an even bigger flat spot?

[rslifkin]

Originally Posted by Dockhead

That's interesting!

But wouldn't that be overcarbed with an even bigger flat spot?

All depends on why the flat spot is there in the first place. Could just be an issue in the setup of the 3.5 carb jetting and other factors that lead to it being different in the 5hp version.

[Celestialsailor]

I think what it is...is that they limit horsepower by carburetion flow. The engine might be able to put out 5hp with a large enough carb. So 5hp is probably the max. Lets say it's a 17mm bore carb for 5hp. They would use a 14mm to achieve 3.5hp and have it achieve a longer life. I believe Tohatsu has a 5 and 6hp outboard that have the same bore and stroke but different carbs.

[rslifkin]

Originally Posted by Celestialsailor

I think what it is...is that they limit horsepower by carburetion flow. The engine might be able to put out 5hp with a large enough carb. So 5hp is probably the max. Lets say it's a 17mm bore carb for 5hp. They would use a 14mm to achieve 3.5hp and have it achieve a longer life. I believe Tohatsu has a 5 and 6hp outboard that have the same bore and stroke but different carbs.

Yup, the larger (123cc) 4/5/6 hp Tohatsus are all the same engine just with different carbs to limit power. With the better flowing carb the 6hp revs a bit higher than the 4 and 5hp versions. I think Suzuki and Yamaha's 4/5/6 hp engines are also the same base engine with different carb, etc. for different outputs. Not sure about Honda (and they don't seem to offer a 6hp anymore anyway).

[sailhand]

The 3.5 tohatsu is a different motor to the 4 5 6 tohatsu motor. I read about this upgrade kit that was available from ready set boat in the US.
https://www.readysetboat.com/mercury...propeller.html
There are also youtube reviews on the kit. I cheaped out and just bought the cheapest 5hp carb on ebay, seems to run fine, plug indicates mixture is good, not too rich or to lean, so far I am very happy with the result. Power to weight ratio of this little motor rivals the better two strokes of old when configured like this. It is in a par with my old 5hp yamaha two stroke and lighter. Long term reliability is yet to be determined.

[MicHughV]

OB engine manufacturer's are smart.

Horsepower (H) is rpm dictated, usually by the formula:

H = T x rpm/5252

Using the same engine, increasing engine rpm by a mere 500 or so can make a 9.9 hp into a 15 hp.

Manufacturers will have you believe you are buying a " bigger" engine and can thus charge you twice as much, when all they've done is change out the jets in the carb.

[jamestaggart007]

Hi Siamese.
Are you still happy with your Tohatsu? Thanks much

[wingssail]

Originally Posted by Dockhead

I kind of like the Portaboat. Would be my second choice if folding RIBs didn't exist.

By "folding rib" you mean the transom folds down?

I have thought about the Achilles folding transom and storing in in a flat bag on the foredeck but my inflatable floor 360 zodiac is lighter, bigger, and faster and stows below.

Anyhow, motors: Our solution won't work for many but we:

• Use a spin halyard to lift the motor w/o rigging block and tackle or swinging out the boom (and we can lift the whole boat and motor that way too in about 1.5 minutes from arrival back to the boat, and do it every night)
• We drop the motor down the bow hatch and store the motor below
• Our 15hp 2-stroke is light and reliable
• For almost any passage we deflate the dingy and stow it below as well
• Our decks stay clear and unobstructed

The fully inflatable is boat NOT as "good" a boat as far as handling goes but it sure stows nicely when back in its bag. It is 15 lbs lighter than a similar (smaller) folding transom ribs or even similar sized length inflatable floor boats.

There are places where 9.9 and 15 HP merc/tohatsu 2 stroke are still sold, and perhaps shipping would be possible. I can buy them here in Mexico.

I will not accept a non-planning boat or one which will not carry two people and a months worth of provision over a mile of choppy water without soaking us and going at 5 knots.

I could not lift a 100lb motor onto its bracket and I would be loath to give up the convenience of our dingy and system, If I have to replace my dingy I will find the boat I want and the motor I want similar to what I have and I'll get them and neither will go on davits since I have no arch (nor will I). There, pretty fixed in my ways aren't I?.

[Celestialsailor]

Originally Posted by wingssail

• Use a spin halyard to lift the motor w/o rigging block and tackle or swinging out the boom (and we can lift the whole boat and motor that way too in about 1.5 minutes from arrival back to the boat, and do it every night)
• We drop the motor down the bow hatch and store the motor below
• Our 15hp 2-stroke is light and reliable
• For almost any passage we deflate the dingy and stow it below as well
• Our decks stay clear and unobstructed

That 15 weighs 90 lbs. So I'm sure you have to be quite careful moving it around on a halyard in anything less than very calm conditions. Admittedly, it was the same for my 6hp. Tohatsu 4 stroke at 55 lbs. moving it by hand after I used my motor hoist to lift it off the dink and pick it up, making my way to the companionway ladder and down. Most of the time I was by myself with no crew.

[wingssail]

Originally Posted by Celestialsailor

[/LIST] That 15 weighs 90 lbs. (nope, I'm wrong, it's 75 lbs. I found it in the shop manual I have) So I'm sure you have to be quite careful moving it around on a halyard in anything less than very calm conditions. Admittedly, it was the same for my 6hp. Tohatsu 4 stroke at 55 lbs. moving it by hand after I used my motor hoist to lift it off the dink and pick it up, making my way to the companionway ladder and down. Most of the time I was by myself with no crew.

No, I believe my old 15 weighs 67 lbs, (nope, I'm wrong, 75 lbs. Found it in the shop manual I have) which is why I am so worried about the newest 4 strokes still at 99lbs or more.

Hoisting with a halyard at a midships position is far easier than lifting at the transom in waves. Once the motor is off the transom of the dingy and hanging next to the hull of the big boat I climb up and walk it around where I want it while Judy, my wife, works the halyard from the cockpit on the big 3spd winch.

The trickiest part is when you first lift it off the dingy. If you don't time it right a roll of the boat can dunk the motor, but we've never done that.

If it is really rough we just yank the entire dingy, boat motor and gas tank, all at once onto the deck of the big boat where it sits until we get to a calm place. It takes about a minute and a half. That way we can skedaddle outa there fast.

[Cheechako]

I haven't bought a 2 stroke outboard for decades. Have they messed them up like they have the gas yard equiptment? Taken user control out?
I bought a brand new Stihl weed whacker and it was impossible to use. Sold it after 3 uses. No choke, no adjust by the user. I spent more time trying to start it than use it. I use only non ethanol fuel too. The chainsaw is a bit better but not much.
OTOH my little 90's 4.5 HP old Mercury outboard (USA) would start in 3 pulls after sitting all winter. Every time.
If you want a usable small 2 Stroke OB buy some Grampa's garage queen lake fishing motor.

[Celestialsailor]

Originally Posted by wingssail

No, I believe my old 15 weighs 67 lbs, (nope, I'm wrong, 75 lbs. Found it in the shop manual I have) which is why I am so worried about the newest 4 strokes still at 99lbs or more.

Hoisting with a halyard at a midships position is far easier than lifting at the transom in waves. Once the motor is off the transom of the dingy and hanging next to the hull of the big boat I climb up and walk it around where I want it while Judy, my wife, works the halyard from the cockpit on the big 3spd winch.

The trickiest part is when you first lift it off the dingy. If you don't time it right a roll of the boat can dunk the motor, but we've never done that.

If it is really rough we just yank the entire dingy, boat motor and gas tank, all at once onto the deck of the big boat where it sits until we get to a calm place. It takes about a minute and a half. That way we can skedaddle outa there fast.

Hi...This is where I found the 90lbs.


https://www.tohatsu.com/marine/int/outboards/M15D2.html