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Old 04 December 2011, 03:42   #11
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Country: UK - Scotland
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Boat name: snagglepuss
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Hard choice this one

4 stroke , no oil, lot less fuel but v v heavy
2 stroke v cheap to buy, faster acceleration but will drink your wallet dry.

re insurance : some companies are ok when you tell them that your are over the limit, they dont say no until you start taking the piss i.e. 30% more. Others will just say no to a 1 gram over the max weight.

your other option is to upgrade your rib!

Dave
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Old 04 December 2011, 04:06   #12
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Originally Posted by clydeoutboards
Hard choice this one

4 stroke , no oil, lot less fuel but v v heavy
2 stroke v cheap to buy, faster acceleration but will drink your wallet dry.

re insurance : some companies are ok when you tell them that your are over the limit, they dont say no until you start taking the piss i.e. 30% more. Others will just say no to a 1 gram over the max weight.

your other option is to upgrade your rib!

Dave
I disagree

My experience with insurance tells me they may say it's ok to overload the transom but try getting that in the cover note. They will take your money but if a claim is needed ??

Of course if it's a theft claim you could argue its not caused any issue but if it was any sort of accident claim they would argue the excess power may have contributed to the accident. I'd not want to be in that position should you hit into another boat, or worse still injure a person etc where your liability side would been needed. Is it worth the risk ?

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007
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Old 04 December 2011, 11:21   #13
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Hi

The boat was built in 2007 and I have just checked the plate and that says 80hp on it.

Cheers
Chris

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Originally Posted by 9D280 View Post
Chris,

Website will, likely show the latest version of the boat. If your hull plate says 2.5Tonnes / 4.5Hp, than that's what your insurance will be basing it on, even although the hull may have been redesignd ten times between the one you have and what you see on the website and wander over the bridge to buy new.

I don't know when your hull was made, but a wee example,, mine was built in 1984. Even Autolube hadn't been invented and most 60s were 2 cyl instead of 3 and so my transom is rated to 110Kg / 60Hp. I'd be pushing it with an Autolube 60Hp Yam! (one of the reasons I have my museum hanging on the transom)

As a good rule of thumb, work out from the plate when it was built, and if it says 80Hp, than at a going in point most 80Hp engines of the time will be spot on for a max engine.

If your hull was built before 2- stroke was banned, any 4- stroke will likely put your transom top precariously close to the water!

Or you could wander over to the dark side & get a nice light 80Hp Clamshell...... woooohahahahahahahaaaaaaaa
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Old 04 December 2011, 13:45   #14
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That would most likely be an 80hp 2 stroke. My bet is its the same transom as the current models but they've now downgraded it to 60hp to take into account that its now only 4 strokes that can be supplied from new.

Peter ~ Boatsandoutboards4sale ~ askboatsandoutboards4sale@sky.com ~ 07930 421007
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Old 05 December 2011, 04:06   #15
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Hi

9D2820 is so right. i would say bring it over and we could try that config but to be honest that is a big jump and not worth the effort.

I would look for a 2 stroke and if its in central Scotland there is a good chance we can meet you at the sellers place if that helps?

Dave
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Old 05 December 2011, 06:06   #16
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Interesting the maker's plate lumps the engine in with the crew & luggage. Implication of that is that in the absense of any other paperwork, you could presumbaly with no bags and assuming Chris weighs a nice average 75Kg put a ton of engine on there!


All joking aside, I went from a roughly 110Kg Yam to an 85 Kg Merc. The difference in handling, time to plane etc was phenomenal. if you can live with the smoke when it's cold, 2- stroke makes a lot of sense.

As for the 2 stroke drinking & 4 not, at WOT or thereabouts there's going tobe naff all in it. To make 80Hp you have to burn the juice. Bottom line 4stroke only becomes economic if you spend lots of time at low revs - and that is because most of them are EFI so can be a bit more efficient at tickover. Same could be said for any of the direct injection 2-strokes.
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Old 05 December 2011, 06:25   #17
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Originally Posted by 9D280 View Post
As for the 2 stroke drinking & 4 not, at WOT or thereabouts there's going tobe naff all in it. To make 80Hp you have to burn the juice. Bottom line 4stroke only becomes economic if you spend lots of time at low revs - and that is because most of them are EFI so can be a bit more efficient at tickover. Same could be said for any of the direct injection 2-strokes.
We need to disagree for the first time on this one. 4 strokes are far better on fuel and on our 90hp we have been running we were getting between 30-50% better econemy.

There are lots of reports on this and so that we are not talking about honda's have a look at

http://www.outboard-motors-and-boati...efficiency.pdf

Dave
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Old 05 December 2011, 06:42   #18
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Do you think it would sit to low in the water with a 75hp 4 stroke?
If you already have the boat it should be easy enough to see the difference at rest. Simply load the back of the boat as far back as possible with the weight difference between your current engine and the proposed one.

Of course there is more to being too heavy at the back than the transom sitting too low at rest. e.g. harder to get on the plane, compensated for by adding more weight up front which means you burn more fuel for no gain...
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Old 06 December 2011, 06:14   #19
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We need to disagree for the first time on this one. 4 strokes are far better on fuel and on our 90hp we have been running we were getting between 30-50% better econemy.

Dave
Running at WOT most of the tiime? I doubt it.

The implication of that is that a couple of weekends ago I could have done Balloch to the Drovers & back on sometwhere between 15-20L of fuel had I a nice shiny 4 stroke 60 on my transom rather than the 31.5L my Clamshell drank for the trip. Even taking a 30% improvement that would mean I would have clocked 0.53L/nautical mile. Anyone got a rib can do that at cruise? (at a 50% improvement it's 0.44L/nt mile!)

Now, if you are mucking about at mid & low throttle a lot, yes, I could believe numbers like that but I did say WOT.....
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Old 07 December 2011, 07:39   #20
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Got a wee bit more time to deep dive this.....

Compare: How many of us actually get the advertised MPG from our cars?

Observations:

1) It's a manufacturer's leaflet. They can't sell 2-stroke any more. It's in their interests to big up 4-st.

2) Quote (page1)
"Data used in the graph was obtained through in-house testing under uniformed conditions.
Results will vary depending upon operating conditions (boat design, size, weight (load), weather, etc.)"

Ok, so they bolted the engines to a clamp, ran them at theoretical optimuim to see how much they drink per hour. then multiply by a lot of hours to make the difference look bigger.

I'd like to see that done independantly on real boats- e.g that "uniformed conditions" test will likely not take into account stuff like Pol said above - you need to burn more fuel to lug the extra weight around amongst other things like appropriate prop pitch for your hull....

3) DT75 / DF70 and DT55 / DF 50
of course it's going to drink more!

4) The distances are in KM. Convert to nautical miles per L and the numbers aren't quite so spectacular. (0.91 Vs 1.07 for the 55/50 test) Also both were run at 4500rpm. Any Suz DT or DF owners like to tell us what their optimal cruising RPM is?

5) the idle numbers are what I said all along. That's where 4 stroke really wins. (well, that and relative silence)



In summary - the numbers look good, but like all numbers that look a little too good to be true, I would treat with caution.

Yes, there will be incremental improvements - Computer flow analysis & the like is improving air - fuel mixing in cylinders all the time - but the same thing is going on with the DI 2- strokes. I'd like to see the same test done on, say a Last generation 'rude 2- stroke 60 and an Etec, or similar comparison on an Opti. Then run the same test with "DI 2- stroke vs 4- stroke". as well as the 2 vs 4 stroke. I.E. a three way comparison. Ideally then duplicated on real boats with data loggers as well to allow a proper comparison and to compare the lab to the waves. What's that pig doing up there......?

Only then will we get a vaguely full picture..... which will then need fine tuned to each & every one of our differently set up RIbs!




Back to Chriis' original Q, Unless you are doing thoosands of hours a year at WOT, there's probably not a lot of difference in running costs.
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