The pros and cons of repowering above the manufacturing max

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I know this subject has been talked about, discussed and debated probably as long as there have been boats with outboards motors on them.

My intention was and is not to advocate, promote or encourage reckless behavior especially to the degree that it might compromise anyone’s personal safety. Nor was it to intentionally hurt anyone feelings, inevitably that happens after all this is an internet forum and often times things get assumed and or lost in the translation . I just put on my big boy pants and laugh it off when it happens to me.

My intent was to try and get some facts regarding “firstly” how a boat manufacturer goes about determining a max HP rating for their hull and to see if my hunch that most manufactures factor in a “cushion if you will” and untimely put a lower max HP placard on their hulls than what the formula would allow for. My hunch has been substantiated. I’ve learned a lot.

In response to a mandate from Congress contained in the Federal Boating Safety Act of 1971 (FBSA), the United States Coast Guard issued regulations covering small outboard boats and the maximum rated horsepower for them. The regulations bind the manufacturer to provide a capacity plate that shows the maximum rated horsepower for each hull.

My interpretation of those regulations is that the manufacturer must state the horsepower as no more than that computed under the formula, except, if the manufacturer conducts the performance testing procedure, the results of that testing can be used (with some qualifiers). However, the manufacturer is apparently free to state a lower rating if desired, and sometimes does. Note that the regulations only require ratings for monohull boats under 20-feet in length.

The formula provided in the regulations reduces to:
(2 X L X W) -90 = rated horsepower

Where:

L=boat length
W=transom width; if the boat does not have a full transom,
the transom width is the broadest beam in the
aftermost quarter length of the boat.

The rated horsepower may be rounded up to the nearest "5".
Here is an example of how the rating formula works in practice, applied to an older Boston Whaler boat, the V-20 model:
Boston Whaler V-20
Length = 19' 10"
Width = 7' 5"

Thus:

(19.83 x 7.42 x 2) - 90 = 204.15
Rounding up = 205 maximum rated horsepower

In the case of the V-20/Outrage 20, from 1978 through 1985 Whaler chose to give it a maximum rating of 180-HP instead of 205-HP. Affixing rating labels which are lower than the rating permitted under the formula is common and that was my whole point. It’s not unreasonable or unsafe to add a few ponies above the max HP placard, and if you’re over 20 ft it’s not even mandated for the manufacture to affix a hp rating placard all though most do.

It’s interesting and note worthy that this federal mandate is only for monohull boats under 20ft. It’s also note worthy that The United States Coast Guard has an opinion on this frequently asked question, and their answer from their website reproduced below:

Can I use a bigger motor on my boat than what it's rated for?
It is not a violation of Coast Guard regulations to install or use an engine larger than specified on the capacity label, but there may be state regulations prohibiting it, and restrictions from your own insurance company regarding this.

There are no Coast Guard regulations against exceeding the safe loading capacity, however, there may be State regulations or restrictions from your insurance company which prohibit this. There is a Coast Guard regulation that gives Coast Guard Boarding Officers the power to terminate the use of a boat (send it back to shore) if, in the judgment of the Boarding Officer, the boat is overloaded. There is no fine for this, unless the operator refuses the Boarding Officer's order.
NOTE: The Coast Guard Capacity Information label is required only on monohull boats less than 20' in length. The label is not required on multi-hull boats, pontoon boats (catamarans), or on any sailboats, canoes, kayaks, or inflatable boats, regardless of length.
 
When I went to get insurance for my boat 2 of the questions asked were
What is the max hp the boat is rated for
what is the hp rating on your motor
I asked them the what if I was over powered and their response was I would not be covered under my policy
The tournament trail that I fish also has a rule about over powered boats.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333605#p333605 said:
redbug » 58 minutes ago[/url]"]When I went to get insurance for my boat 2 of the questions asked were
What is the max hp the boat is rated for
what is the hp rating on your motor
I asked them the what if I was over powered and their response was I would not be covered under my policy
The tournament trail that I fish also has a rule about over powered boats.


You are correct sir,

As mentioned in this thread and my last post “some” insurance companies will not insure your boat if you powered it with a motor that has the capability of producing more ponies than the hull placard states as max HP. From the best I can tell this is not an industry standard.

Some insurance companies don’t contend with it and other just want a higher premium. Funny how it always seems to come down to money and liability................... :LOL2:
I wonder how many guys are insuring there Jon boats.
 
C/D, your formula doesn't compute for 90% of the members of this forum who own smaller hulls.

Mine: 14' x 4' = 56 - 90 = -34 hp Does -34 hp mean I can only paddle?

Please post up the sources for your information because honestly it doesn't pass the smell test and as said above is just going to confuse someone into an unsound situation.

Quick Google search for boat data plates brings up these guys who do replacement decals;

https://garzonstudio.com/boat/capacity-decal.html

Please note that each plate says the same thing about complying with the USCG ratings for HP and load.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333633#p333633 said:
Ranchero50 » 51 minutes ago[/url]"]C/D, your formula doesn't compute for 90% of the members of this forum who own smaller hulls.

Mine: 14' x 4' = 56 - 90 = -34 hp Does -34 hp mean I can only paddle?

Please post up the sources for your information because honestly it doesn't pass the smell test and as said above is just going to confuse someone into an unsound situation.

Quick Google search for boat data plates brings up these guys who do replacement decals;

https://garzonstudio.com/boat/capacity-decal.html

Please note that each plate says the same thing about complying with the USCG ratings for HP and load.

LOL You need remedial math sir,

And possibly some reading lessons as well. As clearly as it can be in the example in my post this is the formula. It's the length times the with times 2 rounded up to the nearest 5 minus 90 So let me help you 14x4=56 56x2=112 rounded up to 115-90=25 Your boat according to this formula should not exceed 25HP. Its not hard, with a little practice I thing you could do it.

Something does stink around here.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333639#p333639 said:
Ranchero50 » 10 minutes ago[/url]"]Yeah, my math sucks, so where is the source?

It does indeed..................... :LOL2:

It's a few hundred pages and I don't have a copy of it my back pocket at the moment. In between trying to save the world maybe you can find a little time to do some of your own research............................ :LOL2:

That's the formula weather you believe it or not, like it or not. Good day sir.
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333643#p333643 said:
redbug » 7 minutes ago[/url]"]I hope to be perfect one day

LMAO ok here comes the childish chit. Ok I'll play along. Surely you can come up with something better than that. It's so easy for me to believe you guys have such and interest in the safety and welfare of the boating community. "really"............ :LOL2:
 
I'm just asking because I'm curious.

Your posts seem to be having anger issues with this thread and even with the formula you still haven't shown why or how whoever came up with it decided to use it.

IBTL?
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333648#p333648 said:
Ranchero50 » 12 minutes ago[/url]"]I'm just asking because I'm curious.

Your posts seem to be having anger issues with this thread and even with the formula you still haven't shown why or how whoever came up with it decided to use it.

IBTL?


I’ll bet you're curious,

Well better that my “posts seem to be having anger issues with this thread” than me having anger issues with it. LOL Let’s see does this pass the smell test. I’m thinking no…………………………………….. :LOL2:
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333659#p333659 said:
Bugpac » Yesterday, 23:18[/url]"]
[url=https://www.tinboats.net/forum/viewtopic.php?p=333655#p333655 said:
SumDumGuy » 14 minutes ago[/url]"]check it...

183.53 Horsepower capacity

https://lmgtfy.com/?q=+183.53+Horsepower+capacity


Per that, the equation that was posted is inaccurate, or rather incomplete, not knowing transom height, and remote steer. :) Excellent reply Sumdumguy. :)


That is the formula in the Federal Boating Safety Act of 1971 (FBSA),

This is from my original post. ". Length, with, transom thickness and height along with the hull materials all factor in. The one thing that is crystal clear is they are always going to error on the side of caution" LxWx2-90 is the base line.
 
I don't think I have ever owned a boat that wasn't overpowered, or at least became overpowered after running it for some time with the max HP stated on the plate.

Notice though, that where I live there is no law against this, and although insurancecompanies can deny any customer on whatever grounds they choose, most don't. In case of an accident, it would be up to the insurancecompany to prove that he accident was caused by to much HP. NB! I'm not in the US.

The only problems I have come a cross with overpowering is weightrelated, not powerrelated. The same sort of issues can easily occure when repowering a boat, going from a (light) 2-stroke to a (heavy) 4-stroke. But I hardly ever see anyone raising their eyebrows when people repower an old boat with a new(-ish) 4-stroke weighing several 10's of kg more then their previous 2-stroke.

A few examples from my own "fleet".
On my (alu) Silver Colibri (405 cm lenght) i run a 4-stroke Honda 50HP, although stated Max HP is 30. I started with a 30HP, wich was good with just me in the boat, boarderline ok with a fishingmate and useless with three in the boat. I'm now on my second 50HP on this boat and I've had it for 13 years. It now does 34 knots with just me, and 32 knots with two people an fishinggear, about 9 and 12 knots better performance then with the 30 HP. Only issue is that with two people sitting at the back bench at the same time, the selfdrain takes on water. Problem is easily solved with a plug.

On my (fiberglass) Guymarine Evada (lenght 540 cm) i run a 4-stroke Suzuki 80HP, and a 4-stroke Tohatsu 6HP kicker, although max stated HP is 70. I started with 60 HP, wich simply couldn't lift the hull enough when on plane so the boat ran on it's nose. Only problem is that with the two engines it's now a litle rear heavy so it's slightly slow to plane. Problem partially solved by moving batteries an gastanks forward in the boat.

The only boat I've owned that needed reinforcing due to overpowering was a 9' John. Stated max 5HP, I ran an 8HP and after 15 years or so of use and abuse this boat started showing microscopical cracks in the welding between the rear bench and the transomplate. This was solved by welding on another plate of alu and a beam going across the transom. This boat is now owned by a friend of mine, still overpowered and well into it's thirtiees. :)

From my point of view, weight (and $) is the only issue with overpowering. Speed is only a problem when/ if the boat/ car/ whatever is used by a fool. But one should check for structural damage like cracks on a regular basis and take care, especially when trailering since this is when the biggest strain is placed on the hull. But this really is something one should do regardless of HP.

Use your head, and be safe. :)
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333672#p333672 said:
Team Colibri » Today, 08:36[/url]"]I don't think I have ever owned a boat that wasn't overpowered, or at least became overpowered after running it for some time with the max HP stated on the plate.

Notice though, that where I live there is no law against this, and although insurancecompanies can deny any customer on whatever grounds they choose, most don't. In case of an accident, it would be up to the insurancecompany to prove that he accident was caused by to much HP. NB! I'm not in the US.

The only problems I have come a cross with overpowering is weightrelated, not powerrelated. The same sort of issues can easily occure when repowering a boat, going from a (light) 2-stroke to a (heavy) 4-stroke. But I hardly ever see anyone raising their eyebrows when people repower an old boat with a new(-ish) 4-stroke weighing several 10's of kg more then their previous 2-stroke.

A few examples from my own "fleet".
On my (alu) Silver Colibri (405 cm lenght) i run a 4-stroke Honda 50HP, although stated Max HP is 30. I started with a 30HP, wich was good with just me in the boat, boarderline ok with a fishingmate and useless with three in the boat. I'm now on my second 50HP on this boat and I've had it for 13 years. It now does 34 knots with just me, and 32 knots with two people an fishinggear, about 9 and 12 knots better performance then with the 30 HP. Only issue is that with two people sitting at the back bench at the same time, the selfdrain takes on water. Problem is easily solved with a plug.

On my (fiberglass) Guymarine Evada (lenght 540 cm) i run a 4-stroke Suzuki 80HP, and a 4-stroke Tohatsu 6HP kicker, although max stated HP is 70. I started with 60 HP, wich simply couldn't lift the hull enough when on plane so the boat ran on it's nose. Only problem is that with the two engines it's now a litle rear heavy so it's slightly slow to plane. Problem partially solved by moving batteries an gastanks forward in the boat.

The only boat I've owned that needed reinforcing due to overpowering was a 9' John. Stated max 5HP, I ran an 8HP and after 15 years or so of use and abuse this boat started showing microscopical cracks in the welding between the rear bench and the transomplate. This was solved by welding on another plate of alu and a beam going across the transom. This boat is now owned by a friend of mine, still overpowered and well into it's thirtiees. :)

From my point of view, weight (and $) is the only issue with overpowering. Speed is only a problem when/ if the boat/ car/ whatever is used by a fool. But one should check for structural damage like cracks on a regular basis and take care, especially when trailering since this is when the biggest strain is placed on the hull. But this really is something one should do regardless of HP.

Use your head, and be safe. :)

Good info good post,

Thanks for your input.............................. =D>
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333655#p333655 said:
SumDumGuy » Yesterday, 23:02[/url]"]check it...

183.53 Horsepower capacity

https://lmgtfy.com/?q=+183.53+Horsepower+capacity

Best post in the thread, it brings facts to ponder... =D>

From Cornell's site https://www.law.cornell.edu/cfr/text/33/183.53

So there is actually a lot more involved in the Max HP game for an O/B powered hull than C/D's basic formula.

Must pass the quick turn test (at WOT I think)

If you can't run over 35mph you can either use (A) the chart and it's various formulas or (B) the max speed test (for 13' or less remote steer)

Per (A), if your L' x W' = <52 you use the chart and if you are running a hard chine hull you rate it one less. So per (A) a 1436 would be 14' x 3' = 42 which is 7.5hp but the hard chine makes it a 5hp limit. Over a factor of 52 with remote steering you double it and divide by 2 - 90. Over a factor 52 flatbottom or hard chine it .5 x factor - 15. Other boats would be .8 x factor -25. So my original MV1448 tiller steer (.5 x 56 = 28 - 15 = 13hp) should have a 15hp limit on the data plate, not the 25 it came with. Weird...

Per (B) they would run the hull over an obstacle avoidance course to see how it handles at WOT.

If you run over 35mph you have to pass the quick turn test (which I think would be really exciting at speed) and pass the avoidance course test.

And it looks like a 13' or below remote steer with a capacity of 2 can be maxed at 40hp.

It also looks like the reg was last updated in 2012.

So per all that I guess the biggest limit to your HP choice is what the hull can handle safely in an 'Oh Crap' situation (which is kind of what I've been saying all along).

Really this is a good group of tests to do just to know if you'll be able to avoid a stump or swimmer while running at speed. When you are loaded, can you kick the tiller hard over at speed and turn 90` without the hull becoming unstable? When loaded can you perform an avoidance maneuver at speed?
 
[url=https://www.tinboats.net/forum/viewtopic.php?p=333687#p333687 said:
Ranchero50 » Today, 10:41[/url]"]
[url=https://www.tinboats.net/forum/viewtopic.php?p=333655#p333655 said:
SumDumGuy » Yesterday, 23:02[/url]"]check it...

183.53 Horsepower capacity

https://lmgtfy.com/?q=+183.53+Horsepower+capacity

Best post in the thread, it brings facts to ponder... =D>

From Cornell's site https://www.law.cornell.edu/cfr/text/33/183.53

So there is actually a lot more involved in the Max HP game for an O/B powered hull than C/D's basic formula.



quote]


LOL no not C/D’s formula "The formula the Federal Boating Safety Act of 1971 (FBSA) as I mentioned" I also mentioned in my very first post in this thread there were other factors.

From my first post " There is a formula that is somewhat standard but it leaves much to the imagination and is open for interpretation. Length, with, transom thickness and height along with the hull materials all factor in. The one thing that is crystal clear is they are always going to error on the side of caution.
 
Well I guess I'm just slow because I'm still not sure how they calculate the hp. In their explanation,
Compute a factor by multiplying the boat length in feet by the maximum transom width in feet excluding handles and other similar fittings, attachments, and extensions.
does this mean the widest point of the transom, as in the top of the transom and not the width at the base? If it does, that might explain how your 1436 is rated higher than a 5hp.
 
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