What hp is best for size of boat

Tormented96

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Mar 31, 2015
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I have a 1990 searay 160 bow rider and it has a 70hp force outboard on it now and I'm wondering what hp size might be best for this boat I'm not looking to be the fastest on the lake but I do want to have the right size motor to push it around
What do you guys think
 

Silvertip

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Look at the maximum horsepower plate. The best HP is whatever that plate says. Don't go less than 70% of that rating.
 

Sea Rider

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If there isn't a visible plate on transom, contact the manufacturer..

Happy Boating
 

JimS123

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If its running OK, the 70 you have now should be more than adequate.
 

hardwater fisherman

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On the boat manufactures page her at iboats it lists 1990 searay boats 160 bowrider has a max hp rating of 125hp.
 

pckeen

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Yes - 70% of 125 is 87.5, so a 125 hp rated boat would need at least a 90.

You can run the boat on less power than that, but it will be harder to get it on plane, and it may not get on plane at all when fully loaded.
 

Tormented96

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Well that's great news so what could I do other than changing to another engine to get it up on plain if it turns out it doesn't maybe a a larger pitch prop?
 

southkogs

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70HP is possibly a little bit underpowered for that boat if it's rate for a 125HP.

What I would do first: Just you in the boat, take it out and get it up on plane. It might simply be a weight issue if you've got the family on board. Make sure you monkey with the trim to see how it reacts at different trim settings.

If it won't plane with just you in the boat, do a simple tune up - mainly clean stuff and make sure the motor is running properly.

If it won't go that way - I would then start thinking it's just slightly under powered.
 

JimS123

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Well that's great news so what could I do other than changing to another engine to get it up on plain if it turns out it doesn't maybe a a larger pitch prop?
I used to own a very similar boat. It came with a 3-cyl 60 HP Evinrude. I later upgraded to a 3-cyl 70 HP Evinrude. Boy I loved that boat and wish I still had it now. It wasn't the fastest on the lake but it ran faster than I wanted or needed to go. We could run with 4 adults and 2 children without a problem at all.

That 70% number is merely an opinion and it has no basis in fact. Prop that 70 so that at WOT you just hit the maximum rpm spec. If you don't know what that number is, google it. If planing is a problem, you need to run a smaller pitch, not a bigger one.

Personally, I prefer to run a cupped SS prop to achieve the best performance. Tell us what your max rpm is, what prop you have on now, and we can tell you what new prop to buy. If you don't have a tach to get the data, buy one. That'll be a lot cheaper than a new motor.

Having said all this, if your 70 is worn out, poorly maintained with bad compression, etc, etc., then optimizing it is a lost cause.
 

Tormented96

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Well I'll tell the story of why I'm asking this question I purchased this boat pretty cheap from a friend of a friend after selling my jet skis because my kids are still to small to enjoy them so I decided to get a boat. Was told the boat had a 90 horse on it before but I blew up so they gutted everything from steering back and got this force 70 but didn't hook it up other than bolt it up to the transom. I took it in to a local marine shop to make sure the motor is good because I couldn't hear it run. So far from what I was told the motor runs and has good compression 137 134 and 127. Carb needs rebuilt and so does fuel pump no big deal I can do those kind of things. The biggest issue I have is they said that for the cable steering cable to hook up the motor needs to be raised a little to clear the bolt on the steering rod or it will drag on the transom. By the looks of things boat was meant to have hydraulic steering. That being said they told me that it may cavitate.
What should I look at to make sure it doesn't cavitate
 

64osby

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A picture of the steering and motor on transom would help.

Boats don't "need" hydraulic steering. It is an upgrade for smooth operation.

A motor is raised or lowered to position the motor for optimum operation, not to adjust the steering connection.

A motor will cavitate if it is mounted too high or if has the wrong prop.
 

ondarvr

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Apr 6, 2005
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They ventilate when mounted too high, cavitation a totally different animal.

Find a different shop, how can they say it runs good, but needs the carb and fuel pump rebuilt. If those aren't right it won't run well.

Without knowing the year of the Force, it should bolt right on and hook up to whatever steering system had been on the boat before. That is unless it's very old and then it would connect with an actual old school
cable, but even then there are adapters.

Is the shaft length correct on the Force for your transom?

Don't put any money into the Force, if it needs work or doesn't fit your actually needs, sell it and get something bigger and better.
 

Silvertip

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I can assure you the 70% figure is a good target, but hull design, boat weight, load, hull cleanliness and condition all play a part in how the boat performs -- not just the power/length ratio. The engine must also be in perfect running condition and making full power. I bought an Alumacraft 165CS some years back and originally powered it with an excellent 40 HP Evinrude that I removed from another of my boats which I sold. Yes -- the 40 would push the boat nicely with two aboard. However, it was a dog out of the hole and speed was not acceptable and various prop and engine height adjustments did little to change this. That boat had a 75HP max rating. I installed a 75HP Merc and the boat turned from a slug to a very nice performer with speed in the 40+ range. 70% of 75 HP is 52.5 HP so you can easily see how the 70% rule affected this boat. 70% of 125 HP is 87.5 HP so in your case the Force is under that target. The boat originally had a 90 because that's what the 70% target suggested it have as a minimum. Performance to one person may not be acceptable to another.
 
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