Ideal dinghy outboard size

[soling42]

Our 100lb, 10'-4" Achilles dinghy with an aluminum rollup floor and inflatable V section crys out more than a 2hp OB for us to get out and about or to lug our gear. The "Ideal" sized OB comes as I ponder too much OB to also manage on our 26' sailboat vs too small to get the dink up on plane with a few people. Could I expect a 6hp Ob to get 3 avg people up on plane fairly easily and run at 10-12kts w/2 people in flat water?

I wouldn't be using it exclusively on my sailboat but also on morning solo fishing runs or evening lake excursions. 8hp weighs in at 83lbs vs 57lbs for the 6hp. I can manage 50lbs but 80+ might make me hesitant to bother.
Thanks for your input.
Mike

 

[Mike B]

We have an Achilles 10.4 with an air floor and an 8hp 2 stroke. It will get 2 people up on plane, but add our 55lb Golden Retriever and it struggles to do the same. I think a 6hp may be too light for what you want to do. Any chance you know someone that will let you use their 6 for a test run?

 

[Freedom77]

Unless your water skiing behind it 4HP should be more that adequate. 6HP will work but as you said, It's about the weight. Fair Winds and Full Sails....

 

[Ted]

I have an 9.5' Achilles with an air floor. My 5hp can just barely get on plane with two adults. My 8 hp will do it easily but I suspect that it would be difficult if not impossible to plane with 3 adults. The most I've carried is one adult and two young adult daughters of less than 100 pounds soaking wet and some light gear. Was able to plane with the 8h with no problem. It's going to be a close call. You might want to look into some of those devices that attach to the transom that help get the boat on plane quicker and at a lower speed.

 

[alexco38]

I have a air cooled 2hp Honda for a 8ft ding. Better than rolling. The motor is only 28lb.

 

[Lee Coller]

In my 9'6" Achilles I can get up on a plane with one adult with 6HP Suzuki, with a second Adult I have on occasion managed a plane, but it requires near perfect conditions. I don't think the 6 will cut it for your requirements.

 

[JVB]

A motor that's too heavy to handle comfortably will be a hazard. One day you will lose your balance or get your foot caught momentarily and that overweight will cause a disaster, especially if you don't have a hand free. Go with a motor that doesn't stretch your strength and balance limits and get a propeller shroud to improve its performance a little
http://shop.sailboatowners.com/prod.php?50097

Having the right propeller will make a big difference too.

 

[jibes138]

I had a similar achilles and with a 4HP 2 stroke Johnson I could plane it with one person but not with two. I doubt 6 HP will plane 3 people at the speeds you expect. The dinghy is probably rated for 8HP or more. An 8HP motor is too heavy to remove to store on your boat without a mechanical lifting device. 2 stroke motors are generally lighter than their 4 stroke equal HP replacements. My 4HP Johnson was light and easy to handle with one hand and install and remove. Any more weight and I would not try it, the dinghy is rocking and unstable so I would absolutely require a lifting aid for any more weight. I was very happy with the 4HP for over 10 years of use.

 

[soling42]

I was leaning toward the 6hp for it's lighter weight but in my mind was pretty sure it'd come up short of my desired speed. Wrestling it onto a storage bracket is always a concern as I really need a bit bigger sailboat(but don't we all) with a nice davit and a bit bigger OB for my Achilles. I think I'll try to bum a 6hp OB from somebody to come up with real world decision.

On my smaller flats boats I'd always install a planning fin that'd mount at the horizontal fin just above the prop to help get it up on plane so maybe I'll give that a try with a more aggressive prop too. Thanks for any and all input on squeezing as much as I can out of the smallest OB. Haven't bought an OB just yet but I'm shopping.
Thanks again, Mike

 

[DannyS]

I admit that I have a cadillac for a dinghy, an 11 footer with a high pressure air floor and a 9.9 hp four stroke. Weight was never an issue since I never even thought about hoisting the thing alone. You have all the mechanical advantage you need with your boom and boom vang. Just attach the vang to the end of the boom and swing it out over the side of the boat to the awaiting motor on the dinghy.
Of course, it sounds as though you want to use the motor for both the dinghy and the mothership. The answer may be to make a boom extension. You could lash the spinnaker pole (if you have one) to the boom so the end of the pole is directly over the mounting bracket for the sailboat. Bring your main halyard down and attach it to the end of the spinnaker pole for support and attach the vang down from that and hoist away.
I use our dinghy to haul me, my wife, two kids and our dog all over the place. I also love to fish from the dinghy and like being able to get to those fishing spots a bit farther away than a 2hp would allow realistically.

 

[Mike B]

My pleasure and good luck!

 

[peterbud]

Re Ideal dingy outboard size

I was leaning toward the 6hp for it's lighter weight but in my mind was pretty sure it'd come up short of my desired speed. Wrestling it onto a storage bracket is always a concern as I really need a bit bigger sailboat(but don't we all) with a nice davit and a bit bigger OB for my Achilles. I think I'll try to bum a 6hp OB from somebody to come up with real world decision.

On my smaller flats boats I'd always install a planning fin that'd mount at the horizontal fin just above the prop to help get it up on plane so maybe I'll give that a try with a more aggressive prop too. Thanks for any and all input on squeezing as much as I can out of the smallest OB. Haven't bought an OB just yet but I'm shopping.
Thanks again, Mike

I currently have a mariner 2 stroke 5hp. I think it is ideal because it is large enough to get my inflatable up on plane with one adult or two small people. But one of the biggest advantages is the fact that it has both an internal and an external tank. I like this in that if I am going cruising I will use the external tank but if i am just running around the harbor I just switch to the internal tank. It also acts as anize emergency reserve if you are cruising. My infatable is a 9.3 ft

 

[soling42]

Danny, I have a yama8hpHT on our sailboat so the OB for our really nice dink is dead wt or at least a backup if my main OB dies. We do many extended trips so a backup seems practical although my Yamaha has run flawless for 6yrs. Really like the spinnaker pole/boom extension. That might solve part of my reluctance with a heavier OB. Great input.

Peter, a 2stroke would be a lighter way to go but I've looked around and they don't make newer ethanol tolerant OBs in a 2stroke in the U.S. anymore and the used ones I've seen were suspect. If I could find a nice one it'd be an option but the Admiral demands reliability.

Thanks for the input, Mike

 

[RichH]

Consider a good used 8HP 2 stroke. 8HP would be the minimum for planing a dink with 2 persons onboard. The 2 stroke would be vastly lighter in weight than a 4 cycle and because the 2 stroke has larger jets and orfices will have less gum/varnish problems than a 4 cycle with 'ethanolated' gasoline.

The 'key' to success in operating any OB is 'run it completely dry' before putting it away for more than a few days. If storing longer than a few weeks, then also totally drain the carb.

 

[Benny17441]

6hp not likely to get you on plane with 3 people. The secret to performance is getting the right prop.

 

[soling42]

Everyone's input along with the thread below was really helpful to sway me away from an expensive mistake with a brand new 6hp OB. It's a long thread but basically it was very clear that the Tohatsu/merc/Nissan 6hp won't cut it when it comes to pushing my Achilles up on plane.

http://www.sailnet.com/forums/gear-maintenance/36963-nissan-tohatsu-6h-4-stroke.html

Now the hunt begins for a decent 8hp 2cyl and a way to hoist it safely on-board utilizing Dannys idea above. Thanks so much and have a great season.
Mike

 

[Steve Dion]

Be sure to check the weight of the engine too when making your choice.

 

[John Nantz]

Be sure to add up all the extras

My experience is with an Avon 3.15 roll-up which doesn't have the hard bottom but is a tad heavier at 115 lbs and with an 8hp 2-cycle.

With this rig and a 3-gallon fuel tank, life jackets, anchor, oars, etc., it can get two people on a plane but start adding in extra fuel, garbage (to shore), food (return from shore), things start getting a little heavy.

With an 8 hp outboard you'll find that the little fuel tank you used on the old outboard will quadruple in size. And then there is the Extra fuel you'll need. Where on the mother ship will all this gasoline be stored? And on a hot day it can give off vapors or really pressurize the tank. Hopefully it's not plastic and there are no sparks nearby.

With three people I think you'll be approaching what I've got and maybe even going past it in total weight. Sure, the hard bottom will help but what I'd like to suggest is see if you can find another boater that will let you test drive their 8 hp outboard on your dink. Invite them along for the weight!

Note: Weight at some point makes a huge difference in planing. A little less and it planes good, a little more and the stern digs in pulling a huge wake behind until one can climb out of the hole. And at wide open throttle you're sucking a LOT of fuel. And let's not even talk about a 9.9.

If the dink is towed with the outboard it causes quite a bit of drag on the mothership. Maybe I'm a little more drag-sensitive than some (have a Max-Prop), but it is a drag. In a seaway it could become a liability back there if it ever flipped. Ouch $$$. Another consideration to think about. Personally, I very seldom tow the dingy with the outboard on it for these reasons, and seldom even tow the dingy.

Personally, after 20 years with this setup I'm seriously thinking about scaling back to a smaller outboard, probably in the 3-hp range or so.

Here is a picture of my dingy lifting setup using a Forespar vang, the largest one they had at the time. Chose that for the line size (easier on the hands) and the line length. Just connect the one block to the main halyard and the other to either the dingy or outboard harness. One can also run the bitter end to a winch if need be. Gives a lot more control over launching and retrieving the outboard. Be sure to keep the outboard from banging onto the side of the hull.

Be sure to consider how many long runs you'll really make and the quantity of fuel and/or number of fuel stops you'll need.