150bhp outboard quicker than a 150bhp inboard ??
Discussion
B16JUS said:
ive just been told that a 150bhp outboard will be quicker than a 150bhp inboard any comments is this true if so how ?
cheers
I would have thought it would weigh less, which may have something to do with it. I have a 4.3 Mercruiser engine and it looks like it's out of a truck, an outboard looks about 1/5th the size. cheers
in that i would agree, OB better... .less weight, less "plumbing", possibly less drag on the hull.
Also its a fairly lightweight boat that does not seem to be too much of a V (i am a little out of date on bow riders and the like so others will have more specific knowledge)
I still would think that 115hp would be a little under powered on that, but your 150 - 190 mentioned should provide more than adequate fun!!!
eta looking at the picture, it looks like with an inboard you would gain a much larger rear sunbaithing deck, is that important?
Yup ... inboard gives you "more boat" .... so a case of horses for courses ....
Also its a fairly lightweight boat that does not seem to be too much of a V (i am a little out of date on bow riders and the like so others will have more specific knowledge)
I still would think that 115hp would be a little under powered on that, but your 150 - 190 mentioned should provide more than adequate fun!!!
eta looking at the picture, it looks like with an inboard you would gain a much larger rear sunbaithing deck, is that important?
Yup ... inboard gives you "more boat" .... so a case of horses for courses ....
Edited by XJSJohn on Monday 9th February 13:36
B16JUS said:
when you say slow for the 115 do you mean top end or will it be slow all round
J
where you will really need the power is pulling it up onto the plane, especially when towing ski's etc.J
You will also be generally working the engine harder.
For example - a mate of mine recently picked up a RIB that is formerly an offshore rescue boat from a ship. It came with a 70hp. The rib will be significantly lighter than your boat, but it will have a deeper V, so will need to reach a higher speed before paining but ...
70 could get it there, and still push it along at 30+ knots once there ... but it was hard work, used more fuel, and made for a very difficult time for tows. It now has a 120hp on it, makes all the difference.
The best bet is to see if you can find similar boats and see / ride in them with their different engines, but my option, go as big as you can ... engine not working as hard then, and instant speed fix.
well, thats my take anyway .... others will have much more experiance of these soet of things ...
The spec for the GT180 lists recommended engine range from 90 to 150. Its a heavy boat - 1500lbs - & that's dry weight, before you load it with engine, fuel, couple of people etc. I suspect the smaller engines are going to be a little disappointing but don't forget the bigger engine are going to be thirsty!
Be worth posting on specialist boating forums to see what feedback you get & then looking around for examples for sale & going to try.
Be worth posting on specialist boating forums to see what feedback you get & then looking around for examples for sale & going to try.
Edited by paintman on Tuesday 10th February 00:57
paintman said:
but don't forget the bigger engine are going to be thirsty!
The op does seem to want to go fast, (after all, this is Pistonheads) and from my experiance, a smaller engine running at 10/10ths is just as juicy as a big engine running at 8/10ths and you still have the option for more power 
(sorry, couldn't resist that ....)
B16JUS said:
ive just been told that a 150bhp outboard will be quicker than a 150bhp inboard any comments is this true if so how ?
cheers
Quicker to do what?cheers
Truth is there is no simple answer. In the old days of 2 stroke outboards being the norm the lighter weight and positioned further back would have generally given more speed. Nowadays with heavy four stroke outboards that save the planet it's not as simple.
Remember that all boating is a compromise. If you want out and out top speed then move as much weight towards the rear of the boat as possible to reduce the wetted area and chuck as large a pitch prop on as you can to match maximum engine revs with highest horsepower rating and you will be there. Obviously outboards are easier to get this weight toward the back.
If you then want to pull a skier or load your boat up with mates then forget it. The skier will experience a lack of pulling power to get him up and if and when he's up he'll have to put up with the boat porpoising and tightening / loosening the rope constantly. Trimming the engine will help but not solve the problems. It won't handle rough water riding as well either but I assume you are not interested in offshore racing
All three types of engine Petrol inboard / 2s petrol / 4s petrol will give very different torque curves which complicates the matter further. What you want is sufficient low end torque to swing a prop, large enough to give that optimum speed, through the heavy load phase of getting on the plane. No gears here so you're reliant on techniques like ventilating the prop to allow it to spin up and develop power.
Inboard or outboard the drive unit will be similar in profile and given mounting at the same height will be just as efficient as each other with the only difference being the final output ratio to match the engine characteristics. (2s petrol will generally rev higher by as much as 50%.) The result of this is that with the same power, same prop and the same weight and location all the engines will give the same speed.
The reality is that the outboard version will likely have the weight placement further back and gain in top end speed, but will require you to move weight around the boat to give a comforatable tow.
^-- Motorvator is evdiently less drunk than i have been and as such has been able to summarise my blatherings into a much better response!!
in summary, what he said, mine's another beer!!
but ... .
questions ....
Do you just want to go quick?
Do you want to do waterskiing?
Do you want to take several mates out?
You where you going to use it (sea / lakes)
etc (see smart words above .... )
in summary, what he said, mine's another beer!!
but ... .
questions ....
Do you just want to go quick?
Do you want to do waterskiing?
Do you want to take several mates out?
You where you going to use it (sea / lakes)
etc (see smart words above .... )
XJSJohn said:
Do you just want to go quick?
Do you want to do waterskiing?
Do you want to take several mates out?
You where you going to use it (sea / lakes)
etc (see smart words above .... )
Quick is good but no silly speeds maby 30-40 ? is this poss with a 115bhp outboard Do you want to do waterskiing?
Do you want to take several mates out?
You where you going to use it (sea / lakes)
etc (see smart words above .... )
not fussed about skiing deff want to pull some inflatables and maby a knee board
prob 4 in total for a day out fun
thinking of keeping on the water at essexmarine which is on the crouch so in and about there and the mouth to sea
thats the other question people go on about flushing there engines when put onto the trailer i used to do this on the jetski doesnt take long but how do you do this when the boat sits on the water all the time in a berth ?
J
B16JUS said:
XJSJohn said:
Do you just want to go quick?
Do you want to do waterskiing?
Do you want to take several mates out?
You where you going to use it (sea / lakes)
etc (see smart words above .... )
Quick is good but no silly speeds maby 30-40 ? is this poss with a 115bhp outboard Do you want to do waterskiing?
Do you want to take several mates out?
You where you going to use it (sea / lakes)
etc (see smart words above .... )
not fussed about skiing deff want to pull some inflatables and maby a knee board
prob 4 in total for a day out fun
thinking of keeping on the water at essexmarine which is on the crouch so in and about there and the mouth to sea
thats the other question people go on about flushing there engines when put onto the trailer i used to do this on the jetski doesnt take long but how do you do this when the boat sits on the water all the time in a berth ?
J
The engine is less of a problem than the hull if you're keeping it afloat. Weed build up will pull ridculous amounts of speed off particularly a small boat like this unless she is antifouled. Antifouling a ski boat is frowned upon when selling.
Inboards (volvo or mercruiser) will have some form of active cathode protection system and as long as the anodes are kept in check you won't have too much problem. Outboards can be stored in a tilted position clear of the water but without flushing through their life won't be very long.
If you're determined to have it on a berth then look at one the berth lifts that they have for sale down there. For my money though I would just keep it in the park and ride and have it launched on demand. Cheaper and less maintenance other than stripping brakes etc out of trailer and you can have them flush it through each time.
Essex marina great, you can always get away from the nasty stuff somewhere there. I keep one of mine afloat there and launch the other casually. You know jeans t shirt sandals that sort of thing before any smart arse gets in.
XJSJohn said:
^-- Motorvator is evdiently less drunk than i have been and as such has been able to summarise my blatherings into a much better response!!
I resemble the remark that I may be sober. With the amount I spend on beer I should be constantly unintelligble.
Edited by MOTORVATOR on Tuesday 10th February 17:31
Rum Runner said:
Get 2 stroke, old school and carbs , go like stink sound ace , easy to fix ,power to weight ratio but major juice issue and hard to get of not for commercial use.
Oh so right I have a 70 Merc it is a dream runs every time I have a 17' ski boat and it does 40knts. quick blast through with the mufs and leave to fade.Gassing Station | Boats, Planes & Trains | Top of Page | What's New | My Stuff