Maximum Outboard Horsepower Capacity (Guide and how-to)

Have a question about your motor? All motor talk and questions go here.
User avatar
mechanicworkman
Posts: 22
Joined: 06 Jun 2011, 23:15
Location: Florissant, Missouri

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by mechanicworkman » 08 Jun 2011, 00:23

OK, I got a 1436Jon Flat bottom

Across the top its 51" or about 4.25 Feet

Across the bottome its 36" 3 Feet

I have 15HP Mercury

Can someone help me figure this out cause i am still a bit confused! I may have figured out it but dont knwo if i even did it right?

Can anyone help!
-----------------------------------------------------------
"The shores of history are littered with the wrecks of civilizations, where once free men trusted their rights and liberty to a wholly centralized government"

Xtremeboats
TCHunter
Posts: 2
Joined: 17 Feb 2010, 19:05

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by TCHunter » 15 Jun 2011, 17:43

Very interesting thread. I image that 2 strokes are lighter than 4 strokes. I have a 1962 Lonestar that I am restoring. The tag says max is 24hp. So how much did a 1962 24 hp 2 stroke weigh?

User avatar
roblj65
Posts: 37
Joined: 28 Jun 2011, 14:36
Location: Bradford, Maine

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by roblj65 » 30 Jun 2011, 22:14

Thanks!
This is great as I was wondering what the max HP was that I could put on my 1962 Starcraft

momof2inmn
Posts: 1
Joined: 31 Jul 2011, 22:03

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by momof2inmn » 31 Jul 2011, 22:14

Wondering if anyone can help answer a question my dad has. He has a 1979 14' aluminum Deep and Wide Lund and he can't read the motor rating number on the boat because of all the wear (he thinks it may say 25 or 35hp). He's had a very old Johnson 15 hp on it for many years and now wants to put a newer 25 hp on.

Can anyone tell me what the motor rating for this boat might be? Also, from some of the posts in this thread it sounds like the rating may be different that what the boat would have said anyway because it is pre-1980.

Thanks for any help you can give. We go to the lake in three weeks and are cutting it close on motor replacement!

Lennyg3
Posts: 200
Joined: 16 Nov 2011, 22:27
Location: NEPA

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Lennyg3 » 03 Dec 2011, 14:55

How does a max hp rating work with a jet? If the boat is rated for max 150hp, does that mean a 150 power head or can I run a 200/140 jet? Is the max hp more of a weight issue or an overpowered issue?
"Many men fish all their lives without ever realizing that it is not the fish they are after."


River rod-HP180 G3 with a 2005 225 Optimax jet

Lake boat-Tracker targa 18 merc 4 stroke

User avatar
Canoeman
Posts: 497
Joined: 05 Aug 2011, 07:13
Location: Up Nort,MN

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Canoeman » 03 Dec 2011, 16:34

Lennyg3 wrote:How does a max hp rating work with a jet? If the boat is rated for max 150hp, does that mean a 150 power head or can I run a 200/140 jet? Is the max hp more of a weight issue or an overpowered issue?
Depends on state laws and insurance and regulations. I know some states go buy the power-head and others by the foot/prop. MN goes by what is stamped on the motor.

Downside is if you overpower your boat and then say you hit and hurt someone or someone gets hurt in your boat you may be liable because you exceeded your manufacturer hp rating.

If you want to be safe contact your hull manufacturer and have them re-rate it for over what your putting on, if they will work with you. If they wont then it is a gamble.

Lennyg3
Posts: 200
Joined: 16 Nov 2011, 22:27
Location: NEPA

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Lennyg3 » 12 Dec 2011, 01:26

Canoeman wrote:
Lennyg3 wrote:How does a max hp rating work with a jet? If the boat is rated for max 150hp, does that mean a 150 power head or can I run a 200/140 jet? Is the max hp more of a weight issue or an overpowered issue?
Depends on state laws and insurance and regulations. I know some states go buy the power-head and others by the foot/prop. MN goes by what is stamped on the motor.

Downside is if you overpower your boat and then say you hit and hurt someone or someone gets hurt in your boat you may be liable because you exceeded your manufacturer hp rating.

If you want to be safe contact your hull manufacturer and have them re-rate it for over what your putting on, if they will work with you. If they wont then it is a gamble.

Well, I got a hold of PA fish and Game, and apparently they go by HP at the foot. The plate rating is 130hp. Now what is the factor for powerhead/jet? some places say 70%, and some say 66%. Being as though they don't make a factory Jet above 150/105 that I know of, which method would I use for say a 175 or 200? I know the general consensus is that a 200 is a 140 at foot, which would put me over, but using the .66 multiple gives me 132@ foot, and I would think legal.
"Many men fish all their lives without ever realizing that it is not the fish they are after."


River rod-HP180 G3 with a 2005 225 Optimax jet

Lake boat-Tracker targa 18 merc 4 stroke

JohnT
Posts: 58
Joined: 08 Aug 2010, 01:02
Location: Northern Panhandle WV

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by JohnT » 17 Mar 2012, 05:12

Ok , I did the math a coupe of times , My boat is a Lowe Bass 170 . It's rated for a 70 hp and when I do the math it come's out to a 115 hp how is this so . Please help !!! Don't get me wrong I would love to throw a 90 hp or a 115 hp on there for some go fast fun ,for sure .

LA_Gas_Man
Posts: 13
Joined: 18 Feb 2012, 03:25

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by LA_Gas_Man » 14 Jun 2012, 00:27

I have a 1988 16' starcraft all welded jon boat, 70" beam, 66" (5.5') wide transom, steering, 20" transom, that came with a 1989 evinrude 40hp. The sticker says its rated for a 35hp. When I first read this post I calculated my numbers and came up with 90 hp. Here are my numbers;

16' long x 5.5' wide = 88
88 x 2 = 176
176 - 90 = 86 rounds up to 90 hp

The 40hp evinrude that was on the boat pushed it ok, but I knew it could definitely handle more hp. After going over these calculations several times, I found a real good deal on a 1986 85hp suzuki.
Dropped it on the boat and it runs real good. Handles great. With the boat loaded w/3 people, tackle, & 6 gallons fuel I got a steady 38 mph on gps.

User avatar
Frogman Ladue
Posts: 239
Joined: 27 Mar 2012, 22:04
Location: ..on any random lake in NE Ohio...

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Frogman Ladue » 14 Jun 2012, 10:23

...odd, should I have a cousol in my boat, it would be rated for -20hp acording to this formula. Tiller would put it at 18hp, factory tag says 30. And, that's doing the math a few times.

User avatar
Lowe 2070 CC
Posts: 261
Joined: 13 Jun 2012, 10:46
Location: Mississippi

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by Lowe 2070 CC » 23 Aug 2012, 10:48

Seems like there is something being lost in the translation with this formula. For example my own situation is:

- Lowe 2070 CC: 20' long, 8' beam, 1,110 pound hull weight, rated for a 115.

- (20 x 8 x 2) - 90 = 230.

So should I really be rated for a 225?? I don't think so (I'm running 50mph now with a 2 stroke 115). My dad runs a 225 on his 22' Ranger glass boat (it pushes 70+ mph).

My old 16' Xpress, factory rated for 60hp, (16 x 6 x 2) - 90 = 102. No way I'd try to run a 90 on that boat.

There has to be something else factored in there that you're missing.

nick4203
Posts: 128
Joined: 31 May 2012, 02:12

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by nick4203 » 23 Aug 2012, 16:30

Lennyg3 wrote:How does a max hp rating work with a jet? If the boat is rated for max 150hp, does that mean a 150 power head or can I run a 200/140 jet? Is the max hp more of a weight issue or an overpowered issue?

200/140 jet? why are jets always stated like this whats it stand for?

jeremy0998
Posts: 10
Joined: 09 Oct 2012, 15:37
Location: Duncannon, Pa

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by jeremy0998 » 09 Oct 2012, 19:07

Jets are always listed like that because there is hp loss when going from a prop to a jet. In the instance of a 200/140 jet, if you were to take off the jet boot and put on a prop, the engine would be rated at 200 hp.

In PA, the restrictions on your plate only pertain to the hp at the propulsion. Like for my boat, which is a 1760, is rated for a 90 hp motor. So, I could put a 115/80 jet on the back but wouldn't because of the weight factor. You would be suprised how much weight is added to the motor as the hp listing goes up.

wired
Posts: 1
Joined: 21 Oct 2012, 00:25

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by wired » 21 Oct 2012, 13:53

There are other difference with the 150/105 mercury motors that just the bolted on jet pumps. The 105 motors have considerably higher ports than standard 150's. much lower compression and are equipped with 5600 RPM rev limiters. I have a fresh rebuilt 2.0 liter 1996 150/105 that I changed the lower to a standard prop lower. Cranking compression was 95 lbs. I milled enough material off the heads to drop the heads CC to 28 CC from 38 CC and still the compression is only up to 110 lbs. The ports are so high its very difficult to build high compression. On the other hand with the high ports it will push a 23 pitch prop to 65 MPH at 6000 RPM.

User avatar
BloodStone
Posts: 259
Joined: 22 Sep 2008, 01:01
Location: USSR-providence of Flint, Mi
Contact:

Maximum Outboard Horsepower Capacity (Guide and how-to)

Post by BloodStone » 22 Jan 2014, 16:50

What about an older aluminum 14.5' L x 5' W Meyers semi-v boat (front looks like a snub nose bullet, totally flat bottom), originally designed for a tiller, middle bench seat removed, side console put in, reinforced sides (braces) with additional flooring & interior transom wood replaced with new 3/4" red oak with a 1982 25 Evinrude on back? And no, I can no longer read the tag. 8-[
"Everyone should believe in something..I believe I'll go Fishing"
Ernest Hemingway

Post Reply