Dinghy power thoughts

Hey all, hoping to get your thoughts on what to power a dinghy with.

A little background - I'm "practicing" up north on the Mississippi and St. Croix rivers up in MN/WI. Currently have a 30 foot cruiser. We are generally weekend cruisers (2 small kids) with several long weekends and 1-2 week long trips per year.

I'd love to get a Highfield 310 Classic PVC dink. Tiller steer only. Part of the appeal is backwater exploring, fishing, just general messing around. 15 to 20 mile trips to neighboring towns for fun a possibility too. Not sure how I'd move it with the boat yet, towing is easy (slow), and haven't thought a lot about the davit thing yet. Anyway, really after opinions on powering a dinghy.

The Highfield 310 is rated for 20HP max. I've got an old mid 80's Mariner 8HP, and while I may start with that, not sure long term that will suffice.

Dinghy dealer (that's all he sells, 2-3 brands) says most guys put on 9.9 Merc's.

9.9 Merc - 84lbs.
15 Merc EFI - 99lbs.
20 Merc EFI - 99lbs.

The 15/20 Merc EFI's are brand new, and the same engine, same weight. Magical pixie dust makes the 20HP a 20 somehow...don't care really.

Is it nuts to get the 20HP? I'm pretending price isn't a concern. Will the dink be a death trap, and sketchy to run at WOT? Or will I be happy with the extra oomph (I'm not a small dude) and top end speed for those longer fun runs? Another concern is youth handling of it, right now my son is 6, I can see another 6 he'd want to take it out on his own. Should I be sticking to the lower HP to build in a safety factor?

Thanks for your awesome opinions. I'm a trawler wanna-be. Like I said, currently practicing via cruiser.

Thanks!

Within the same outboard class, HP often increases when the manufacturer increases the upper limit or the RPM and more fuel. I would start with what you have and change as you see the need. In a perfect world, borrowing a 15 and 20 HP engines would be the best way to determine what you need.

Ted

It has little to do with HP, but I would GREATLY favor an EFI engine over a carburetor. In my experience they are much, much less prone to fuel problems when left unused for prolonged time, like over the winter.


Now that said, I'd be a bit leery of any vendor's brand new model. I prefer things that have a few years of proof behind them.


As for HP, I'd probably go for the 15 or the 20. With any load, I expect it will be hard to get the 8/9 up on a plane. With one person the 15/20 will probably be grossly over powered, but with 2 people plus gear, it would still be nice to be able to get up on plane..



As for your kid, I wonder if there are devices to limit the throttle? That would guard against a sudden, unexpected goose of the throttle that could end in disaster, and give him time to get progressively more comfortable operating the boat. With just him in the boat, it would be easy to get in trouble with a 15/20hp. And be certain to always use the engine kill lanyard. If you have ever seen a run-away boat where the operator got tossed out, you will never run without a lanyard again.

The 9.9 will seem a little weak when you have two or more people on the boat ,the 15 and the 20 weigh the same. If we're up to me in the money was not an issue I would go with the 20

If the dinghy capacity rating plate says 20, 20 should be OK.

If you ever intend to lift the thing, solve that before you buy the dinghy and motor. Really important!

EFI good, carbs suck. (Or not, as the case may be.)

Weight is an issue if you intend to mount and dismount the outboard often... or depending on whether you decide to lift it... and in that case, HOW you will lift it (motor attached? or not?). Some models are slightly lighter in weight than others -- maybe the Suzuki DF20A, for example, which is also an EFI system; they were lighter at least when they were introduced. (Not a recommendation, just an observation... although we have a DF15A and it seems to work well enough.)

Or if you never intend to lift it, might put it on a trailer for winter, etc... then weight might not be such a big deal.

I dunno about Highfields, but I can tell you an internal "floor" is nice... I wouldn't go backwards on that feature again, FWIW...

As for safety with kids... a 15 and a 20 on that weight dinghy are equal... both can make that dink get squirelly in a heartbeat, so you'll have to solve that with training or other external solutions.

Were it me, I'd probably start with what you have while you think about it... and then if I were to go larger, I'd likely go with whatever the max on the capacity plate says.

-Chris

mncruiser said:

Is it nuts to get the 20HP?

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No, not only is it not nuts and given your size and 15 to 20 mile possible trips, it's a good choice!

I weigh 240lbs. and have a 20hp Honda on my dink that goes faster than I want to.

I like more horsepower and like EFI. However, there's another item you stated quickly and I want to comment on. Thinking to your your safety and to your son in the future, I would not go with tiller only. I want a steering console. As others stated, obviously a kill cord is in order. I don't want 20 hp on a tiller.

Def go with the 15 or 20, and def EFI.

Does the Merc EFI require a battery? My Suzuki 15hp EFI is battery-free which is nice.

Here's how I solved my similar conundrum on my 34. It's a 3.3m/10'11" PVC soft bottom dink that's rated for max 15HP. I run it with a 15HP 2-stroke Merc and it's very stable and can reach speeds up to 20 mph. 10-15 is a comfortable cruising speed for this setup. The Garhauer lifting davit works great for lifting the motor and dink.

http://www.trawlerforum.com/forums/s24/34-lrc-motor-lifting-davit-transom-mount-32080.html

Since then, I have added a dinghy float referenced and pictured here.

Trawler Forum - View Single Post - PVC vs Hypalon dinghy

We have an 8hp on an AB Lammina 9.5. I think it is rated for a 15. The 8hp (Mercury) came with the mothership, otherwise I would have been eyeing a 15.

The 8 performs fine. It is very quiet and very fuel efficient. We can do 16 knots on plane. Would still go with a 15...

I definitely would go with the largest HP that the manufacturer allows, but I also would go with a dinghy that has a console. I can't imagine handling a tiller for a 15-20 mile trip. I would think that if you had to hang onto a tiller for that long it would be a painful experience and you would stop taking longer trips because of the inconvenience and pain involved with the tiller.


The longest trip we have taken with our Whaler is 60 miles round trip. If I had to hang onto a tiller for that long I'd probably never had done it. Tillers are just not comfortable.


My suggestion is to buy the dinghy you REALLY want then buy a davit system that will handle it.

How far and how fast do you want to go? I replaced a 2 cycle outboard with an electric and am very happy. It's quiet, no more carrying gas, and no mixing of the fuel.

I can go about 10 kts in a Livingston w/55lbs. of thrust. If I want to go far, I take a 2nd battery, but have never used it.
As others said, know what weight you're going to lift before installing davits.

I'm going to second (or third, fourth...) what others have said here. The only reasons to not go with the 20 are cost and weight. As it weighs the same as the 15hp, to me if you can handle the weight of the bigger block go with the 20hp. That's exactly what I did with our current setup, a 20hp EFI suzuki that replaced a 15hp carb 2 stroke. It's on an 11' Caribe light.


It's honestly pretty easy to handle a 20 on a tiller, you can quickly and easily adjust the tightness of the steering so there is no feedback. I run our dinghy on long freedive trips all the time, generally 5 to 10 miles, but sometimes longer, it's not so bad. Twenty miles may be pushing it, that's pretty far in a small boat. The thing that gets me after a long trip is more my back from sitting down and banging in the seas, not the size weight of the motor.

If you haven’t taken these trips yet- stick with what you have and get a feel for what you really need. I had a blast with my 3.5 on our little river in WI- and never stayed out long to go very far- buying more power would have been overkill. I’m glad I didn’t as I moved the main boat and didn’t need the dinghy any more...

Whether you go with a 20,15, or even a 10 hp outboard, buy it with a flatter pitched prop than standard and consider adding a Doel Fin.

Some years ago with a 9.9 hp Toahatsu 2 cycle on a 9.5' RIB I couldn't get up on plane with more than one person aboard. I changed the prop to a flatter pitched one and that helped. A Doel Fin helped even more, about equal to the flatter pitch. After both changes I could easily plane with 350 lbs of people, a 40 lb dog, 30 lbs of groceries and 50 lbs of gas.

With today's 4 cycle engines which inherently have less low speed torque, it is even more important to use a flatter pitch prop which lets the engine rev up into its higher torque zone to get up on plane easier.

David

I would go with the higher hp. Keep your 8 hp for when you want your child to run the boat or pick up a trolling motor for the kids to learn with before you let them loose with the larger motor.

I've been running a Highfield 360 Classic with a 20hp Suzuki tiller for the past 3 years. Great little boat. I run 18kts lightly loaded and will plane with 4 adults and 2 kids in salt water, but won't quite do it in freshwater with that much load.

PVC is fine for up north, but if you plan on taking it to warmer climates spring for the hypalon.

EFI is a game changer- almost all fuel problems go away, significantly better fuel economy at less than full throttle cruising. I'll never own another outboard without EFI.

Something i've learned owning a dozen smaller fishing boats... Always install max hp.


The manufacture wouldn't rate it at 20hp if it was going to be dangerous.

Here's an article that helped inform me, basically bigger isn't always better, there are other factors to consider as well:

https://www.powerequipmentdirect.com/stories/1399-How-to-Size-an-Outboard-Motor-to-a-Dinghy.html

Since you have an 8hp motor already, try it with that and see how it does. Go from there.

rsn48 said:

Here's an article that helped inform me, basically bigger isn't always better, there are other factors to consider as well:

https://www.powerequipmentdirect.com/stories/1399-How-to-Size-an-Outboard-Motor-to-a-Dinghy.html

Click to expand...

Wifey B: Omg......as so often stated by those who don't have it....

Sorry, couldn't resist.

On outboards specifically sometimes it makes sense to look at the sizes and the hp and if adding hp involves a lot of additional size and weight maybe not worth it, but if the same basic motor has hp options then might as well go for it. Our only outboards we have triple 300 hp instead of 350 hp simply because the performance tests showed very little upside for a lot of additional weight. 200 lbs per motor difference.

Now, for the dinghy if looking at Yamaha, 20 weighs 126 lbs, 15 weights 111. 9.9 weighs 87. Not much difference between 15 and 20, but then another brand may be even less and worth considering.

Now, our table is ready for dinner. Bye bye.

All of the people recommending you go with something smaller... went with something smaller.

All of the people that are recommending going with something larger (including the female participant... ) are those that went larger.

Go figure...

I grew up with tillers from 7.5 Johnson, to 9.9 Evinrude, and then 25 Yammy... all before the age of 10.

Safety will be 90% in the training of the kid on safe boat handling. And yes, I know, kids will be kids when out of eyesight and will push it... but even said, proper training will kick in even then. As said before, in a small dingy, a helm station will keep the odds way down on horsing around turning bad, vs. the tiller.

Get the 20 hp. There's a 100% chance you won't regret it.

If you get the smaller one, there'll be a 100% chance you WILL regret it... but you'll be telling the next guy that asks the question on here that you're happy with your 9.9 hp....

Flybull,
With displacement boats there’s such an extremely narrow range of what would be propper amount of power it could well be one number. And that number would be about 3hp per ton. For a small boat double that and anything else would be a mistake.

For SD and planing it’s way different. However comparing production boats one can usually find an owner and evaluate the performance seen and take w a grain of salt what is claimed or said.
And if you only have a maximum load once a year you can forget about powering for that event. No need to have more power than you need 99% of the time. But you shouldn’t underpower to the point where you’re overloading the engine frequently.
So the name of the game (power wise) should be to get what you need and no more. More than what you need is stupid.

That said there are wants that are justifiable. In my own case I may use a 6hp OB on my 12’ FD boat and that is way too much. The reason would be to get neutral and reverse gear.

If you are going to be able to leave the motor on the tender, go big. If you are going to be putting it on and taking it off, get enough to beat the currents and plan on anchoring closer to your destination. Man handling a motor in and out (or on and off) of your boat to mount it and store it IS a big deal. If you can lift your launch out of the water with motor attached the game changes. My two cents...

We have a Suzuki 20HP EFI for 3 years now, love it!

Nomad Willy said:

Flybull,
With displacement boats there’s such an extremely narrow range of what would be propper amount of power it could well be one number. And that number would be about 3hp per ton. For a small boat double that and anything else would be a mistake.

For SD and planing it’s way different. However comparing production boats one can usually find an owner and evaluate the performance seen and take w a grain of salt what is claimed or said.
And if you only have a maximum load once a year you can forget about powering for that event. No need to have more power than you need 99% of the time. But you shouldn’t underpower to the point where you’re overloading the engine frequently.
So the name of the game (power wise) should be to get what you need and no more. More than what you need is stupid.

That said there are wants that are justifiable. In my own case I may use a 6hp OB on my 12’ FD boat and that is way too much. The reason would be to get neutral and reverse gear.

Click to expand...

All excellent information, Willy...

And considering your thought process above, I'd still be of the same opinion for the OP to go with the 20hp.

Here's my reasoning... the OP says he's not a small guy. He said "we" and two small kids. He's also interested in exploring the Mississippi river where he currently boats, including possibly some 20 mile trips to other towns to explore.

Two adults, two kids, a small cooler for the trip and a bag of other "stuff" (wives are great at packing bags of "stuff" for excursion), along with a little fishing gear... and that 310 is loaded, with a shorter, smaller planing surface.
Add in the oftentimes strong currents of the Mississippi, especially during high water times, and power becomes your best buddy.

The 15 hp is only 15 lbs. heavier than the 9.9 hp. The 9.9 would be the "underpowered" part of your equation IMHO.

The 20 hp. and the 15 hp. weigh the same. This is because it is the identical piece of machinery (all Merc small OB's are produced by Tohatsu up to and including the 40 hp. I think). The 15 hp. is just a de-tuned 20.

The 15 hp. would probably be the sweet spot in your parameters, but unless the 20 is a ridiculously higher price than the 15, it's a no-brainer in my opinion.

The kids will get bigger. And if the OP is anything like most of us... so will he.

20 hp on a 3.10 dink? Isn't that a little like putting a Hemi in a Prius?

Seriously, if you need your dink to "plane", tow a 250 hp bass boat, and you won't be disappointed.

I put a 9.9 Penta on a 310 Zodiac, and at full throttle, that was enough to flip it way before it came up to a plane.

Sorry, but I always thought powered dinks were meant to get from point A to point B in a timely manner without having to row. I never thought of them as long-distance excursion boats.

My current dink is a 9' wooden rowboat with a 2.5 hp 2-cycle folding shaft Evinrude from the '50s, and while it does smoke a bit, it gets me where I want to go and only weighs about 20 lbs.

Jacques Burgalat said:

Sorry, but I always thought powered dinks were meant to get from point A to point B in a timely manner without having to row. I never thought of them as long-distance excursion boats.

.

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Wifey B: Then you never thought of their full potential.

We sometimes cover a hundred miles of cruising around in a RIB. That's like some of the incredible beauty of the keys that we can't get to see in other ways.

BandB said:

Wifey B: Then you never thought of their full potential.

We sometimes cover a hundred miles of cruising around in a RIB. That's like some of the incredible beauty of the keys that we can't get to see in other ways.

Click to expand...

OK, I get it, but where do you put the Port-a-Potty?

The point I was trying to make was that this trend to overpower everything boggles me. For example, who needs a pair of 350 HP diesels to push around a full displacement 40' plastic trawler with a 12 knot hull speed? That's the kind of power you used to see in harbor tugs, and that your commercial trawlers never came close to having.

You'll have to admit that extrapolating it to a 20 HP 10' dingy isn't that far of a stretch.

Jacques Burgalat said:

OK, I get it, but where do you put the Port-a-Potty?

The point I was trying to make was that this trend to overpower everything boggles me. For example, who needs a pair of 350 HP diesels to push around a full displacement 40' plastic trawler with a 12 knot hull speed? That's the kind of power you used to see in harbor tugs, and that your commercial trawlers never came close to having.

You'll have to admit that extrapolating it to a 20 HP 10' dingy isn't that far of a stretch.

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Wifey B: Oops...we have 100 hp on an 11' RIB. WOT is 42 knots. Guess you don't approve. Bad bad bad.

I like speed. We were on a 116' AB earlier this week, hit 55 knots.

But then our boat at the lake before we moved to FL would top 50 knots.

It's 4:30 AM. I just woke up. Going to wake hubby in a minute, but how shall I do it.