exceeding inflatable outboard hp rating

[ELC]

In the USA, Gulf Coast. It's in the very fine print on most policies. Especially if it's in a state where the law makes it illegal to exceed the rating on the plate.

If you're in one of those states they don't even need the fine print. They can successfully argue that you were operating the vessel illegally which voids the insurance.

Not saying I agree or disagree but simply what I have witnessed happen.

[MicHughV]

most rubber duck dinks will perform well in relatively calm water....but 1-2' chop not so much..where the tendency will be to slow down for better comfort, less spray and ride-ability...negating the need for a bigger, heavier engine...
most people (and passengers) ride their dinks, seated on the inflatable tube, many stand, so this adds to the speed and safety factor issue...quite common to see 3-4 people, all standing, in a moving dink...just to avoid getting wet..
lastly, removing a big outboard from the dink to the mothership can be a pain in the rear end...
I love my 8 hp 2-stroke yammie...does everything I need...planes fine with 1-2 people, which is 90% of the time, it won't plane with 3-4 people, but I wouldn't want to plane anyway...and I can pick it up with one hand....try do that with a 15 hp engine...

[Montanan]

FYI:

As to the USCG.

For any outboard-powered boat over 20 feet in length, the maximum horsepower rating is essentially at the discretion of the boat builder. If the boat is less than 20 feet long, the power rating is determined by a formula.

For remote-steering boats, the formula is: (stern width in decimal feet x length in decimal feet x 2) – 90 = max. horsepower.

For tiller-steer boats with a flat bottom, like a jon boat: (W x L x 0.5) – 15 = max. horsepower

For all other tiller-steer boats: (W x L X 0.8) – 25 = max. horsepower


Read article at this link for more information and the reasoning.

https://www.boats.com/resources/outb...r-steer-boats/

[docrn]

I have a Highfield UL 260 with the larger 17" tubes that is rated for a 6hp. It's only 8.5' long and weighs about 70lbs empty. By myself the boat can do about 14mph with the 6hp. If I put another person in it won't plane so I'm going to find the lightest 9.9 there and go with that. The next model up (UL290) is rated for 10hp and is only one foot longer and weighs 16 pounds more.

I was told by a dealer that the only real difference between the two models is the length and that the transoms and hull thickness on both models are the same. He said it's the shorter length that makes mine not track as well in chop at higher speeds, which I can understand. I'm not looking to race the thing just want to get my wife and the groceries on a step and that's it. Obviously I'll drive it at a safe speed for whatever conditions may arise. That said I am very curious how fast it will go in the right conditions.

[MicHughV]

just remember that the difference between a 9.9 and 15 is pure marketing...
the 9.9 gets slightly smaller jets resulting in a loss of about 500 rpm as compared to the 15...and thus you get 9.9 hp...besides that...same engine.....same weight.....same everything....oh yeah...different hp decal...ha ha...not the same price though...at the end of the day...the 15 will give slightly better top end speed than the 9.9 going flat out, because it can reach higher rpm, but seeing as you are not likely to be running flat out most of the time, it's a $$$ decision...not a hp decision.......

[smj]

Originally Posted by MicHughV

just remember that the difference between a 9.9 and 15 is pure marketing...

the 9.9 gets slightly smaller jets resulting in a loss of about 500 rpm as compared to the 15...and thus you get 9.9 hp...besides that...same engine.....same weight.....same everything....oh yeah...different hp decal...ha ha...not the same price though...at the end of the day...the 15 will give slightly better top end speed than the 9.9 going flat out, because it can reach higher rpm, but seeing as you are not likely to be running flat out most of the time, it's a $$$ decision...not a hp decision.......

Not so with Yamahas. The Yamaha 9.9 shares the same block as the Yamaha 8hp, the Yamaha 15hp is a much larger more powerful engine.

[wingssail]

Originally Posted by MicHughV

I love my 8 hp 2-stroke yammie...does everything I need...planes fine with 1-2 people, which is 90% of the time, it won't plane with 3-4 people, but I wouldn't want to plane anyway...and I can pick it up with one hand....try do that with a 15 hp engine...

I lift my 15hp with a spin halyard, so easy, then it is lowered down a bow hatch to the bracket on the bulkhead in the shop. (actually my wife does it, I just guide it).

We did this for years with a 25hp engine, Granted it was a light, 2 stroke Merc. but, still, its easy.

Never try to lift a motor by hand from a dingy to a boat.

[a64pilot]

A few comments, first the HP rating has nothing to do with the strength of the transom or anything else. It’s simply a formula of width and length, some dinghies could be unsafe, some not.
We woud all like to think that a manufacturer has done testing and analysis to determine what’s safe and what isn’t, but unfortunately that’s not the case, the limit is not determined by the manufacturer, but at least in the case of a US boat, it’s determined by a government agency that does no testing in individual boats.
Secondly the HP rating of a motor is not marketing, it’s actually the HP the motor is capable of, yes for example the 9.9 Suzuki thru 20 HP are all the same block etc and weigh the same and are the same physical size, but the HP is really different, you can think of it as a 15HP souped up to 20 HP and detuned to 9.9 if you want to, but the HP is actually different.

Finally, my Wife’s car is roughly 600ish HP, will turn I believe 12 sec 1/4 mile times and has a top speed approaching 200 MPH.
But we don’t do any of that, it’s fine to get groceries in it, and nothing requires us to do burn outs in Public’s parking lot. My last motorcycle topped out at 300 KPH, but I didn’t jump on the highway and run 300 KPH.

In both instances it’s nice to have reserve power, but nothing requires us to run wide open, if you can restrain yourself in an auto or on a bike, why couldn’t you in a dinghy?

If I could have another 10 HP without any increase in weight, I’d certainly take it, that way I could easily get onto plane at a weight I can’t now without underpropping, and cruise at the same speed at a much more leisurely RPM. Actually the relaxed RPM is why I’d want it.
I cruise our sailboat at 1800 RPM when we motor just for the relaxed feeling the lower RPM gives me.

[Jammer]

Originally Posted by Montanan

FYI:

As to the USCG.

For any outboard-powered boat over 20 feet in length, the maximum horsepower rating is essentially at the discretion of the boat builder. If the boat is less than 20 feet long, the power rating is determined by a formula.

For remote-steering boats, the formula is: (stern width in decimal feet x length in decimal feet x 2) – 90 = max. horsepower.

For tiller-steer boats with a flat bottom, like a jon boat: (W x L x 0.5) – 15 = max. horsepower

For all other tiller-steer boats: (W x L X 0.8) – 25 = max. horsepower


Read article at this link for more information and the reasoning.

https://www.boats.com/resources/outb...r-steer-boats/

Inflatable boats are exempt from the formula and can have any rating, or no rating at all, at their manufacturer's discretion, as are sailboats, canoes, kayaks, multihull boats, and (as you point out) boats over 20'.

[zboss]

Take into consideration other operational factors of a heavy large engine:

- Try lifting a 25 HP or 30 HP engine up on your engine mount vs. a 15.
- Ask your wife to trim the engine up when beaching.
- Determine if your mounting equipment (like a rail mount) is OK to deal with all that extra weight on the rail in heavy weather.

- If you have a boat that doesn't require you to remove the engine for passages think about how all that extra weight on the davits impacts your performance.

So on and so forth.

I always thought that a factor on HP was that HP was generally related to weight of the engine and thrust potential and how the transom was engineered to handle the power without cracking or failing.

[Nicholson58]

We have a 15 2-st on a Carib 9.5, rated for 15. It’s a screamer with an empty dinghy and one person. Two people and groceries and it will not plane. 18 or 20 with a lower pitch prop would be better.

[mikedefieslife]

Originally Posted by Nicholson58

We have a 15 2-st on a Carib 9.5, rated for 15. It’s a screamer with an empty dinghy and one person. Two people and groceries and it will not plane. 18 or 20 with a lower pitch prop would be better.

I doubt you had 50-60kg of groceries so I would say there is something wrong with your outboard then. I have seen a 15hp Yamaha plane with three people and was faster than me on my own in with my 8hp unit doing 14kts. Both were 2.6m dinghies with inflatable tubes and aluminium floor, so actually slower than an equivalent inflatable floor dinghy

[MicHughV]

I've often been involved in " impromptu" dinghy races....get some rum going, mouths start wagging...and the next you know...the race is on.....from the anchorage out to some agreed spot...the results have always been interesting...as it has been a " run what you brung" race...the biggest engine was not always the first back...sea state has to be contended with plus a myriad of other little things...a lot of times, dinks had to be " rescued" for one reason or another...never even made it back to the finish line....big talk....little walk....at the end of the day, was as happy then as am now with 8 hp-2st

'jes sayin'.......

[a64pilot]

Originally Posted by Jammer

Inflatable boats are exempt from the formula and can have any rating, or no rating at all, at their manufacturer's discretion, as are sailboats, canoes, kayaks, multihull boats, and (as you point out) boats over 20'.

Where does it say RIB’s are exempt?
What do you mean by inflatable boat, and where are they exempted?

[Montanan]

Originally Posted by Jammer

Inflatable boats are exempt from the formula and can have any rating, or no rating at all, at their manufacturer's discretion, as are sailboats, canoes, kayaks, multihull boats, and (as you point out) boats over 20'.

Ah, indeed your are correct. Thanks for denoting such.


https://www.govinfo.gov/content/pkg/...-sec183-43.pdf

USA Code Federal Regulations

Subpart D—Safe Powering
§ 183.51 Applicability.

This subpart applies to monohull boats less than 20 feet in length, except sailboats, canoes, kayaks, and inflatable boats, that are designed or intended to use one or more outboard motors for propulsion.