horse power

[spiderg]

Hi Guys

Got a question, don't know if it's a dumb one or not regarding bigger engines. If a boat is suggested to be suitable for a 20hp engine and you put a 60hp engine on it, would it be a simple case of giving the engine 1/3 throttle to reduce the hp, My new boat is recommended for 50hp but owners suggest that 20hp is enough. My thoughts are on fuel consumption. I wondered if it was simple maths or more technical.

Gerard

[Keith.P]

I think its just a recommendation by the manufacturer of the boat to what the transom and hull can manage as far as HP.
I have see some boats that are recommended for 50hp and had 120hp put on them and its also a weight issue, I have an 8hp motor that weighs about the some as my 50hp Merc, so its more of a guideline, keep it small and cheap.

[david doyle]

In Short NO you cannot control the HP rating with the throttle.

What motor do you currently own for that boat? That is the one you probabley need.

There is alot to consider but at the end of the day Horsepower and speed make a boat a crap load safer then some poking slow lug, you do not want to be under powered ! RE fuel consumption you might burn more fuel in the 20 operating at the upper RPM range then in the 50 in the bottom end?
I would not bother worrying too much about fuel consumption if you do that you will need to get rid of your Seagulls.

[Collector Inspector]

If a boat hull has a 50 Hp "Recommendation" then maybe 60 would be OK.

If a boat hull has 50Hp as a maximum (Along with number of people and or max weight load) I would tend to stay at 50Hp.

As pointed out the Hp is what is noted for the construction of the hull and transom.

I know some people do some really silly things with overpowering hulls on YouTube for laughs. Watch some of them and you might think and post a comment like "Idiot" or similar.

Boating is meant to be safe.

And as noted, under powering can get you into trouble as well.

As an aside ....I thought to re_power my Savage runabout "Basha" with a 30 Etec. The boat is rated 35HP crankshaft. The Etec is rated 30 prop which is OK as I would only lose maybe 2Hp at the prop. Problem was and is the weight of the Etec over my older engine on the transom. The transom is 1984 vintage. I hung back so to speak.

Engine dealers are very happy to sell modern heavier engines to anybody with a hull............................without checking the weight factor.

B

[skyetoyman]

If your boat is a displacement hull (which it is) then speed is a function of waterline length. A recommended engine hp may not produce more speed than a 20hp but will be producing hull speed at lower revs and thus better fuel consumption , less stressed. It doesn't work for seagulls as they like to work hard. General rec is 2/3 max hp is about right.

[spiderg]

Thanks for the help. I'm getting the boat moved this week so I'll post pics then hopefully you guys will help me with your knowledge on add ons. It requires a bit of paint and the windows put back in, but I hope to maybe add some navigation lights and stuff, so you're help will be appreciated.

Gerard
Really looking forward to it. 56yrs old and first real boat, ha ha.