Outboard sizing Q??

[Hurricane_Ditka]

New to the forum, slightly new to boating, and posting this at work so I don't have time to search older posts...

Anyways, I have a old '78 alumacraft that is rated for a 25hp outboard and had heard that some older outboards of different hp had the same weight with only minor changes. My question is what is the biggest motor I can put on my boat? The previous owner was using a 40 hp.

 

[lncoop]

Re: Outboard sizing Q??

Alumacrafts are good boats. What size is it? Welcome to iboats.

 

[coolguy147]

Re: Outboard sizing Q??

rated for 25hp you use 25hp.

 

[Hurricane_Ditka]

Re: Outboard sizing Q??

It's a 16' V.

And I was wondering if the weights of the motors were the same between a 25 and 30 or 40 Hp. It seems easier to get a slightly larger motor for a better price used in my area.

And yes, I know the "use what it's rated for", but if the weight is the same.....

 

[indy440]

Re: Outboard sizing Q??

its not just the weight, its also the force that it will be putting against the transom.

That being said, I wouldn't hesitate to put a 40hp on it if it already had one!

 

[Andy in NY]

Re: Outboard sizing Q??

its not just the weight, its also the force that it will be putting against the transom.

That being said, I wouldn't hesitate to put a 40hp on it if it already had one!

i would, if the boats not rated for it. just because the previous owner had a 40 on it doesnt make it safe!

 

[Hurricane_Ditka]

Re: Outboard sizing Q??

I understand the physics of it and that the Recommended size of the motor is there for saftey reasons.

All I wanted to know is what the weight differences were between the different size hp motors if they're all 2-strokes

 

[indy440]

Re: Outboard sizing Q??

weight differences probably vary from manufacturer to manufacturer, you might be able to look up specific numbers if you know exactly the year and model of the motors.

 

[JB]

Re: Outboard sizing Q??

Weight is only a small part of rating a boat for safe HP.

Putting 40HP on a boat rated for 25 would be a very bad decision.

If those guys were stupid they wouldn't have been building Alumacrafts.

Stick to 25 or less HP.

 

[sturdavj]

Re: Outboard sizing Q??

I have not seen a ratio between motor HP and motor weight. There are to many variables that can affect motor weight to be able to come close enough to compile a list.

For what it's worth?.

Do yourself a favor and stay in the range your boat is rated for. Enjoy your boat, don't spend time boating on the water wondering what might happen if you have surpassed the safety threshold. (Been there, done that. Believe me it's not as fun as it might seem? a friends boat, not mine)

Boats are not like cars,bikes or quads, you do not want to pull a smaller motor simply to replace it with a bigger motor. This will not provide "better performance'.

To increase performance check out the prop section in this forum.

Good Luck & safe boating

 

[ClassyGlassy]

Re: Outboard sizing Q??

I don't look at what the motor says it is, I look at what the actual HP is! Motors before about '86 were rated at the powerhead and not at the prop whereas '86 and newer motors were more often than not rated at the prop making true listed HP.

My '76 Merc 1500 says 150hp but is actually about 125-135hp at the prop. My boat is rated at 120hp......so I put the 1500 on it instead of the 1150! Keeping within reason to the boat rating isn't going to get you in trouble.

I think 40hp would be my max on your boat......stay closer to 30 or 35 if you can.

 

[IronOutlaw]

Re: Outboard sizing Q??

Every 40 I've seen is alot bigger than a 25. I think a 30 or 35 would be ok especially if it had a forty on it before. I believe most mercury 40s are 4 bangers but not sure on other brands. I know my 55 Johnson 2 cyl is alot heavier than my grandpas 25 merc 2 cyl. Alot has to do with the lower unit being alOt more heavyduty.

I def wouldn't put a four cylinder on there IMO.

 

[Hurricane_Ditka]

Re: Outboard sizing Q??

Thanks to the last two posters for giving me useful information.

Once again, all I wanted to know was what the weight differences were

 

[Andy in NY]

Re: Outboard sizing Q??

not to beat a dead horse, but actually the question was:

New to the forum, slightly new to boating, and posting this at work so I don't have time to search older posts...

Anyways, I have a old '78 alumacraft that is rated for a 25hp outboard and had heard that some older outboards of different hp had the same weight with only minor changes. My question is what is the biggest motor I can put on my boat? The previous owner was using a 40 hp.

 

[JB]

Re: Outboard sizing Q??

Accept advice or suggestions that involve any outboard over 25HP, regardless of weight, only from those who accept liability for any bad result.

 

[Hurricane_Ditka]

Re: Outboard sizing Q??

It's ok. We got a 50 HP motor on it just a little bit ago I got real cheap. Works great, just had the boat out

 

[JB]

Re: Outboard sizing Q??

Really glad you sought the advice of experienced and expert boaters, Ditka.

But I don't understand why.

 

[bob johnson]

Re: Outboard sizing Q??

this is a very dynamic subject....

with seemingly conflicting facts....

I have a 2070 boat that came as a tiller....it is rated for 60 hp.

they make a side console and a center console of the same exact boat..I looked at the center console on the lot and saw that the transom brackets were in fact the same as on my boat!!!!

I removed the rear bench seat and installed flooring and floatation under side benches that i added and I added a center console...

the factory center console is rated for 115 hp... same hull, same transom...

MAYBE the rear decking might stiffen the rear, who knows..i think it is the aspect of where the boat is manned.

thats 55 hp difference!!!!!!!!!!

I also own a 1969 16 foot ALUMACRAFT v hull utility with bench seats and a small side console( dont know if original or not) the boat is a closed bow from the factory..it is set up for remote control...i think the tag was 40 hp...

it is unreadable now days...

this is a thin .070" thick hulled boat...has some bracing at the transom...cant believe it is much different than the OPs.

i bet the difference in rating comes from how the boat is operated( tiller VS remote)

thats it..

the integrity of the boat is the same either way..


they make commercial boats with no rating tag...

you have to use your best judgement..

as for adbvice, i cant fault anyone for saying stay within what the tag recomends..

but new stuff is invented from doing things outside the NORM...

tehn it becomes standard... funny how that is

bob

 

[sturdavj]

Re: Outboard sizing Q??

Great job Ditka,

?please give me a call when you take your boat out. I want to be sure to remain at home, one recovery effort was enough for me?.

 

[JB]

Re: Outboard sizing Q??

Yes. Where the helm is makes a lot of difference. Often the same hull is rated for twice the HP as a remote steered boat over a tiller. Center of moment, center of gravity, etc. The classic Boston Whaler 13 is rated for 20HP as a tiller boat and 40HP as a console boat.

The point is that trying to outsmart the engineers who built a boat is about as smart as trying brain surgery with a chainsaw. Most people have no idea what factors are involved in keeping a boat safe.

There is no fact, none, that makes it anything but stupid to overpower a boat, God help you at 100%.