9.9 Max- can i go more HP?

Outdoorsman said:

Here is the formula taken form the US Coast Guard Backyard Boat Builders Regulations (Just do a google search)...

Kinda technical...but if you exceed Max. HP Limit, your insurance will not pay for any claims if that boat was in an accident and someone got hurt.. not to mention you would not have a leg to stand on in civil court,,,,

Sec. 183.53—Horsepower capacity
The maximum horsepower capacity marked on a boat must not exceed the horsepower capacity
determined by the computation method discussed in paragraph (a) of this section, or for certain
qualifying boats, the performance test method discussed in paragraph (b) of this section.
(a) The maximum horsepower capacity must be computed as follows:
USCG 2003 BOATBUILDER’S HANDBOOK | PART 1
58
(1) 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. If
the boat does not have a full transom, the transom width is the broadest beam in the
aftermost quarter length of the boat.
(2) Locate horsepower capacity corresponding to the factor in Table 183.53.
(3) For a boat with a factor over 52.5, if the horsepower capacity calculated in Table
183.53 is not an exact multiple of 5, it may be raised to the next exact multiple of 5.
(4) For flat bottom hard chine boats with a factor of 52 or less, the horsepower
capacity must be reduced by one horsepower capacity increment in Table 183.53.
Table 183.53—Outboard Boat Horsepower Capacity
[Compute: Factor = Boat Length X Transom Width]
If factor (nearest integer) is 0-35 36-39 40-42 43-45 46-52
Horsepower Capacity is 3 5 7.5 10 15
[Note: For flat bottom hard chine boats, with factor of 52 or less, reduce one capacity limit (e.g. 5 to 3)]
No remote steering, or less than 20[sec] transom
If factor is over 52.5 and height
the boat has
Remote steering and at
least 20[sec] transom For flat bottom hard chine
boats
For other boats
Horsepower capacity is
(raise to nearest multiple
of 5).
(2 X Factor)-90 (0.5 X Factor)-15 (0.8 X Factor)-2

Outdoorsman

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FuzzyGrub said:

Outside the liability issue, running a 2 stroke 15HP should not require any transom mods. The 2 stroke 15hp, develop the extra hp at higher rpms. The max torque applied to the transom will be getting on plane, where the 15 will have the same torque as a 10.

Now, going larger hp, or a heavier 4 stroke, beefing the transom is advisable.

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flatboat said:

see, i wonder about that. i have 3 hulls that are clasified as , comercial ' they don't have a bia plak' just a red warning tag telling you they don't meet cg specs . the boats really don't have a hp power rating,i mean you can't put a 75 on a 14 footer but i know a lot of people running 40 hp 3cyl mercs on em . but i would check with the insurance co just to be sure .

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Thanks, I am interested in a 4hp motor. What transom mods do you recommend? Beefing up gussets and stuff?

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gouran01 said:

my boat weighs right around 130 LBs dry with nothing in it, 12 ft flat bottom. with 10HP 2stroke weighin in about 75 LBs she cruises at 21MPH with just me. Absolutely not too manuverable at those speeds but gets from A to B in a hurrray! Debending on your hull, a semi v would probably do well on plane with a 10 but 15-20 would probaby get ya similar speeds. Lil boats sure are fun!

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Jay D said:

The valco's I use to see were pretty stout boats, I am sure a 15hp 2 stroke would work fine. My 14' richline w/9.9 puts it on plain at 12 mph with me alone. I think if you went to a 15 it would push your 12' great.

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bpoulin said:

What I'd do is research what 9.9's are actually 15's with a smaller carb, then put the bigger carb on. Possibly even bring it in to the shop to see if it can get bored over and get a bigger piston in it. This way the cowl still says 9.9, and you can run it on restricted lakes :wink:

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FuzzyGrub said:

Just let that 4hp screem! OK I'm betting you ment 40. I have no experience in over powering by that much. Just make sure you attach that lanyard during the testing phase.

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nomowork said:

My 13 1/2 foot Gregor has a maximum hp rating of 20. I sold the 20hp Johnson that it came with and bought a brand new 15hp four stroke Honda. I didn't weigh it but it was heavier to mount than the old 2 stroke. I think a 9.9 would have been adequate in my case but oh well.

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aeviaanah said:

nomowork said:

My 13 1/2 foot Gregor has a maximum hp rating of 20. I sold the 20hp Johnson that it came with and bought a brand new 15hp four stroke Honda. I didn't weigh it but it was heavier to mount than the old 2 stroke. I think a 9.9 would have been adequate in my case but oh well.

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How fast that 15hp goin?

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nomowork said:

aeviaanah said:

nomowork said:

My 13 1/2 foot Gregor has a maximum hp rating of 20. I sold the 20hp Johnson that it came with and bought a brand new 15hp four stroke Honda. I didn't weigh it but it was heavier to mount than the old 2 stroke. I think a 9.9 would have been adequate in my case but oh well.

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How fast that 15hp goin?

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Oh it'll go fast enough for me. I'm still in the break in period and have only ran it a few times in the water but it's plenty fast enough to get the job done. I have it trimmed up to the highest setting to help keep the boat level and that's with a passenger in the front.

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sirbeigealot said:

My 14' Valco has a 7.5.
It seems to be adequate, but someday I'd like to get something bigger.

Check this out:
https://youtu.be/koNjVSNk4v0

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