Question about hp rating

[troutbum1982]

I am going through and fixing up a 50's model crestliner, long story short it is 15' and according to the information I dug up it is rated for up to a 60 hp outboard. To me this sounds insane, so I am just curious what the difference in ratings are from 40 years ago to present. I am thinking a 35-40 hp...... but I even wonder about that. Just would like some input.

 

[kwik_uk]

Re: Question about hp rating

I've got a 16.5' Dateline, which is rated at 60HP. This was complete rubbish and the boat had a 115 Merc tower of power on it for years. It's being replaced with a 135HP V6.

Take it with a pinch of salt unless insurance says otherwise.

 

[Teamster]

Re: Question about hp rating

I think the way outboard engine horsepower is rated was changed sometime in the 1980's,....

Prior to that horsepower was measured at the crank,.

After that it is measured at the prop,...

Someone please correct me if I am wrong,........

 

[Woodonglass]

Re: Question about hp rating

Here's what I found on the subject...

[Code of Federal Regulations]
[Title 33, Volume 2, Parts 125 to 199]
[Revised as of July 1, 1999]
From the U.S. Government Printing Office via GPO Access
[CITE: 33CFR183.53]

[Page 754-757]

NAVIGABLE WATERS

CHAPTER I--COAST GUARD, DEPARTMENT OF TRANSPORTATION (CONTINUED)

PART 183--BOATS AND ASSOCIATED EQUIPMENT--Table of Contents

Subpart D--Safe Powering

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:

[[Page 755]]

(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" transom
Remote steering and at height
If factor is over 52.5 and the boat least 20" transom -------------------------------------------------
has height For flat bottom hard
chine boats For other boats
------------------------------------------------------------------------------------------------------------
Horsepower capacity is (raise to (2 X Factor) -90....... (0.5 X Factor) -15..... (0.8 X Factor) -25
nearest multiple of 5).


I have a 1961 Lonestar Glass boat witha 20" Transom and the Plate says she's rated for a 70hp. I have a 40 hp on her and with 4 adults she's gunna be WAY underpowered. I will in the future be putting a 70' on her. I would think your boat could handle the 60 with no problems at all

 

[GT1000000]

Re: Question about hp rating

This is quite confusing stuff, but as WoG has noted the CG rules, I have read through them several times to try to make heads or tails out of "regulation speak"...

Using my particular boat and My interpretation of what the regs say...this is what I came up with...


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.

In my boats case the transom is NOT full width, so if I am reading this correctly, the BEAM, as measured somewhere near the back quarter is the number to use...in my case, this equals 7.5 Feet times the length, 17 Feet...equals a factor of 127.5

Using what I think is the correct Factor...2XFactor minus 90=HP rating...which in my case comes out to...
127.5 X 2=255-90=165 HP

Does that make sense???

Anybody? Buehler?

Realistically it does seem very close to being correct for my style boat, but since it never had a capacity plate when I bought it, and the company who made them originally, doesn't exist...I guess, my guess, is a good guess...

 

[andgott]

Re: Question about hp rating

60 HP isn't too out of line for a 15' boat- My '60 Glasspar was 'rated' to carry 75 HP from the manufacturer, though it wasn't even available at the time. Later models with the same hull were rated higher. I've got a Merc 850 on mine (85 HP), with no problems.

35-40 certainly won't be too much, and I think there will be times you'll wish you had a bit more... Though if you're putting a vintage motor on it one of the lark or 'big twin' type johhny-rudes with the right prop would probably push her along nicely.

If it were mine, I'd look at the 50 hp or so range.

 

[Cadwelder]

Re: Question about hp rating

Horse power rating has been discussed here many times. From working at a boat factory (back in the early 80's so I'm sure things have changed) I know the engineers worked calculations quite carefully on the HP rating. I know for a fact NorrisCraft would come up with the rating the engineers said and then they would take the boat out with that HP and see how it performed, they would make all kinds of notes and then increase the HP until the boat became unstable at top end, more notes and testing.

So in short, I'm a firm believer that the MAX rating is what should be on most any boat to get it's peak performance. Now I've seen many many boats way overated and they perform quite well, (there is a safety factor figured in from the factory). The recommendation here on the forum is stick with the name plate and no more, but that's a liability thing. Also if your boat is insured you'll need to stick within the nameplate rating or there could be problems with them paying a claim should there be a problem.

I ran a 17' ProCraft for years (rated for max 120) with a 150 Mercury and never had any issues of any kind.....

My 2 cents..

CW

 

[Mygreenihc]

Re: Question about hp rating

This thread is great. Props to Troutbum for the post and to Woody for the information. Is Woody a regular encyclopedia or what?

I want to add a question to this. Does a jack plate add to the length? I know that Ranger, and a few others, started building an engine mount on back of some of their bass boat hulls that offset the engine by about a foot, and I believe that it is considered length. Does anyone know if you could add the distance taken up by the jack plate to the boat length?

Thanks,
Brad

 

[Teamster]

Re: Question about hp rating

I am going through and fixing up a 50's model crestliner, long story short it is 15' and according to the information I dug up it is rated for up to a 60 hp outboard. To me this sounds insane, so I am just curious what the difference in ratings are from 40 years ago to present. I am thinking a 35-40 hp...... but I even wonder about that. Just would like some input.

I think the way outboard engine horsepower is rated was changed sometime in the 1980's,....

Prior to that horsepower was measured at the crank,.

After that it is measured at the prop,...

Someone please correct me if I am wrong,........

To rephrase what I was thinking/trying to say,........

An old 60 horse of the vintage your talking about is probably like a 40 or 45 horse modern outboard,.....Due to the change in the rating of outboard horsepower,....