Comparing outboards power to inboards

Joined
Mar 16, 2005
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13
I was just curious if you take a boat about 18 ft. in length with, say a 305 inboard with 200 horsepower that will run 55mph. What size of outboard motor will it take to push that boat the same speed? :cool:
 
Joined
Mar 16, 2005
Messages
13
Re: Comparing outboards power to inboards

I was also wondering how much lighter would the outboard be? rough estimate Thanks for any comments
 

Silvertip

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Sep 22, 2003
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28,771
Re: Comparing outboards power to inboards

305/350 Chevy bare is about 575#. Add to that a couple hundred pounds of out drive, manifolds and accessories and you are approaching 950# or so. A 200 HP two-stroke outboard is about half that weight and takes up far less room (important in an 18 footer). The outboard is also far easier to service since you can stand next to it rather than laying on your belly trying to work in an extremely tight area. If you are getting 55 MPH with a 305, the boat is fairly light so 200 HP outboard would outrun it as well as get better hole shot. I would be guessing but I suspect some 150 - 175 HP outboards would do the job.
 

Texasmark

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Dec 20, 2005
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Re: Comparing outboards power to inboards

Agree with up in smoke. Also you don't have to worry about cast iron corroding, trying to get your oil changed, repairing the rubber exhaust that takes engine exhaust out to the outdrive, less of a fire hazard, easier to trailer with the lighter weight, lower inintial cost....to name a few of reasons.<br /><br />Today's loop charged engines are very competetive with I/O engines so fueling is not the issue it was back in the early days of boating where outboards got a (well deserved) bad name for being gas guzzlers.<br /><br />Taking 500# off the *** end of your boat goes a long way toward getting the thing on plane also....knowing how people like to sit in the back seats.<br /><br />Now the kicker. In my boat, you couldn't see the outdrive from the helm. Did not have a position indicator and if I would have, who knows if it was aligned properly or stayed that way.<br /><br />When you are trying to manuever your boat, being it docking or loading on the trailer, you have no idea as to which way the drive unit is pointing. So when you give her the gas you can be in for big surprises. Same thing goes for tilt and trim, you never really never know where the outdrive is positioned unless you leave the helm and go and look. Most outboards, you can see from the helm so it's a no brainer.......and since there is no counter balance, the outdrive is very hard on hydraulics and are very easy to leak down....and since you can't see it you don't know it till it's too late.<br /><br />My 2c,<br /><br />Mark
 

tommays

Admiral
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Jul 4, 2004
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6,768
Re: Comparing outboards power to inboards

This is like and oil debate<br /><br />I feel that older outboards had a huge advantage in ease of care compared to and I/O<br /><br />If you look at a NEW 200 HP outboard that advantage is LONG GONE its as complex as complex gets<br /><br />tommays
 

Silvertip

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Sep 22, 2003
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28,771
Re: Comparing outboards power to inboards

Granted -- the older motors were simpler to service than the new computer controlled motors. However, even in the good old days most people left serious maintenance to their local shop. The same holds true today. Some people can change plugs, lower unit lub, filters, oil changes etc., but most don't because they either don't know how or don't want to be bothered. That really is a moot point however since the new motors simply require less "tinkering". I've owned both and there is no way I'd ever go back to an I/O. Labor is labor whether you do the work or a shop -- only the shop charges a lot more than you charge yourself.
 

tashasdaddy

Honorary Moderator Emeritus
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Nov 11, 2005
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51,019
Re: Comparing outboards power to inboards

i'm trying to sell my first and last I/O. never again even if it's free. and this one was.
 

steelespike

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Apr 26, 2002
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19,069
Re: Comparing outboards power to inboards

In my youth I spent every summer on the St Lawrence river.I weighed maybe 135lbs.I tried lots of times to get up on skis behind outboards from 18 to 50 horsepower on relatively light boats.I never even got close.This with experienced drivers and instruction.Finally tried behind a 20 year old 18 ft wooden Chris Craft with a straight drive old Flat head 6 95 hp engine with a 3,500 max rpm.This boat probably weighed close to a ton with a spotter and driver.I popped up instantly <br />no unbelieveable strain or yanking just smooth powerful pull.Of course an I/O has too much weight in the stern to do this especially if you figure it at 95 hp.But there is no substitute for cubic inches and low end torque.
 

Texasmark

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Dec 20, 2005
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Re: Comparing outboards power to inboards

Hey steele,<br /><br />I tried to learn to ski behind an 18 also. Tried all one summer and didn't make it. Came back the next year and popped up the first try. Same boat and engine, same water. But I don't know how we did it with that puny hp; maybe cause we were 50# sopping wet. Grin.<br /><br />Having the engine in the center of that CC made the difference. It didn't have to plane out in conventional wisdom; it was already planed out; all it had to do was increase it's speed; so like you said, you had a smooth steady pull.<br /><br />Wonder why the pro ski boys and girls today use that type boat? You just answered it.<br /><br />The OB or I/O has to get that heavy bu-tox up on top before it can get going.<br /><br />For what it's worth, a vented prop is super for popping skiers out. My last bu-tox heavy basser was vented and it would pop you right up in a flash.<br /><br />Mark
 
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