Small ski boat questions

[Odhran]

Hi, I've been looking at a few speedboats eg 15/16 ft fletchers for doing a bit of towing rings/skiing etc. Most are equiped with 55-75hp engines. The majority of which being 2 stroke engines. What sort of fuel consumption would one expect from these engines? Better than jetski's fuel wise? Also what sort of servicing / maintenance work would be needed on boats such as these? Looking at boats in around the £2-4k end of the scale, just a bit of cheap fun really.

[cjs]

I asked a boating friend and he reckons on a gallon/hour but a lot less if you run flat out! He gets about the same from his 115hp Honda 4 stroke.

[TFatC]

I think you would be pottering about to only use a gallon an hour with a two stroke of that size.

I run a Shetland Sheltie (best small boat about IMHO) with a Mariner 75 2 stroke on the back. Normal "high speed" running, about 75% throttle on the plain you are looking at 15 to 20 litres an hour.

Waterskiing, you can easily get through 25 to 30 litres an hour, and often more, especially with beginners on the skis.

[MOTORVATOR]

The rule of thumb with 2 stroke outboards is 10% of rated horsepower = american gallons (3.78l)

So expect a 2st 75 hp at full chat to be burning 7.5 us gall/hour or (3.78 X 7.5) around 25 litres per hour.

As you only have a single gear (prop), for your purposes you can work that back down the torque curve to get consumptions at other revs but that doesn't hold true for say race calculations.

Oh and you get rid of shed loads everytime you open the throttle for acceleration, so a skier that you have to keep coming around for and giving the pull will cost you twice as much as one that just gets up and skiis.

Edited by MOTORVATOR on Wednesday 13th July 19:33

[55AMG]

I have a ski race boat with a 115 HP 2stroke mercury outboard. It burns about 25ltrs per hour at 25mph so with a built in 100ltr tank it's good for about four hours. This is similar to consumption quoted on the mercury website. Flat out it drinks fuel!
There isn't much to go wrong with outboards as long as you keep the fuel/oil mix right and the battery charged. The only trouble I've had was as a result of a bag in the water wrapping itself around the propellor. All it should really need is plugs. Four strokes now come with electronic fuel injection and are much more complicated. This makes them better for the environment as the don't deposit oil in the water everytime they are used.
I have ran the same outfit for almost twenty years and everything is running well. Just had the upholstry recovered so it looks brand new.

Happy boating

[55AMG]

Ps. The 50 HP end is a bit weak for skiing with adults but children are fine. It should pull inflatables without any problem.

[danyeates]

cjs said:

I asked a boating friend and he reckons on a gallon/hour but a lot less if you run flat out! He gets about the same from his 115hp Honda 4 stroke.

He gets a gallon an hour from his Honda 115hp four stroke? I find that a bit hard to believe TBH. My F115 would do about 10-13 litres an hour when cruising (according to the ECU). My F150 Yamaha does about 18-20 litres an hour when cruising. You could easily double that when flat out.

I'd say a 55-75hp old two stroke would be similar consumption, but it really will climb when you're skiing as apposed to cruising.

[richardxjr]

Budget £1 per mile for fuel & oil on a 2 stroke 70hp+. Same for my 155hp 2 stroke ski.

Unless flat out everywhere then add 50%


Edit: a 4 stroke Yamaha VX110 ski will halve that. Forced induction 4 strokes will be worse.

For your budget, also look at the Avon Searider 4m RIB with a 50 on the back. Tough, great fun, easy to look after & personalise, there's some great ones over on rib.net.

Edited by richardxjr on Thursday 14th July 11:11

[danyeates]

richardxjr said:

For your budget, also look at the Avon Searider 4m RIB with a 50 on the back. Tough, great fun, easy to look after & personalise, there's some great ones over on rib.net.

Edited by richardxjr on Thursday 14th July 11:11

That's a good idea. I have 3 for sale!

[richardxjr]

SR4s are a great boat. I see you've got them with either speedboat seats/screen or consoles. Most rip the seats out and put a console in - much better in a bouncy RIB plus more deck space.

Someone got a bargain: went for £1500 iirc http://www.ebay.co.uk/itm/inflatable-rib-boat-/250...

[Odhran]

Thanks for the replies folks! Gives somewhat of an insight. They sound jus as thirsty as a jetski then. I was under the impression they'd be easier run! What about a small ~5m rib with a 50hp 4 stroke? Seen a few around for the £5k mark. Would these give as much boating pleasure? They seem a lot more stable (safer?) as I've never had a boat before and always wanted one

[55AMG]

2nd hand jet skis are often a nightmare. They are thrashed to bits and rarely maintained/serviced as they should be. There are plenty of horror stories floating round our Yatch Club of repair bills costing more than the original purchase price.
Every boat is a compromise so pick the one that does what you need and you'll have plenty of fun!

[richardxjr]

Odhran said:

Thanks for the replies folks! Gives somewhat of an insight. They sound jus as thirsty as a jetski then. I was under the impression they'd be easier run! What about a small ~5m rib with a 50hp 4 stroke? Seen a few around for the £5k mark. Would these give as much boating pleasure? They seem a lot more stable (safer?) as I've never had a boat before and always wanted one

Still prefer 2 stroke by far. Better power:weight and a peaky power delivery makes for more fun and a much lower purchase price. A 50 won't ruin you!

SR4m + 50 2T is great, even a 40 copes. Going bigger will mean a bigger engine and consequently higher costs.

SR4.7 is the next step up, again very well regarded. Both easy to sell on each year as you go bigger