Balbas
Well-Known Member
I can only guess that it's because it's generating power twice as often. But then that doesn't make sense as power is a function of torque and time.
Outboard engine Size
- Thread starter FlyingGoose
- Start date
I can only guess that it's because it's generating power twice as often. But then that doesn't make sense as power is a function of torque and time.
FlyingGoose
Well-Known Member
Thanks for the input , worth looking into , some 2 strokes come up on Used sites so will keep my eye on it.
thanks to the rest for your thoughts.
Balbas
Well-Known Member
There are many used 2 strokes available second hand, but the newest of them (if originally sold in the UK) is now what - probably 5 years old? Absolutely fine if you get a low hours well cared for and serviced example. But then they're really quite expensive.
I believe you can still but 2T outboards brand new in the Channel Islands as they're not 'in Europe'.
Airscrew
Well-Known Member
In principal, they are the same.
Meaning if 2 manufacturers claim the same HP (and measured in the same way, they will both be 5hp, more or less.
The major difference is in 'specific' output.
If a 2 stroke and a 4 stroke both had the same cc, the 2 stroke would develop 2x the power, because it 'fires' twice as frequently.
But more relevant to this thread, if we look at the weights (ignoring cooling for a moment) then 2 engines both weighing (say) 20kg, the 2 stroke will develop 2x the power for your 20kg.
CLB
Well-Known Member
More like 12 years old. The Eu regs that stopped their sale in the UK came in in 2006. The last of them probably sold during 2007.
dunedin
Well-Known Member
What size is the mother ship? I wonder if the tender may simply be too big and that downsizing the tender, and outboard, might save a lot of hassle. We have 2.7m dinghy with small 2.5hp 2-stroke outboard, plus davits, to avoid the back breaking effort of previous tender storage.
Depends quite a bit also on where cruising - some places like the Carribbean then a biggish tender and outboard is useful as tend to be travelling a fair way from an anchorage and tend to tie up dinghies afloat; places like Scotland often shorter distances ashore, and often no docks so need to be able to lift boat and outboard up the rocks and back, which can be. Adair hike due to the tide; Baltic and Med weight is less of an issue as less tide.
Depends quite a bit also on where cruising - some places like the Carribbean then a biggish tender and outboard is useful as tend to be travelling a fair way from an anchorage and tend to tie up dinghies afloat; places like Scotland often shorter distances ashore, and often no docks so need to be able to lift boat and outboard up the rocks and back, which can be. Adair hike due to the tide; Baltic and Med weight is less of an issue as less tide.
geem
Well-Known Member
We wouldnt be without our big tender and outboard. You can fit transom wheels if you need to move the tender up a tidal beach. I guess it depends on how you see your tender. If all you ever do is go a few yards from the yacht to the shore then size is less important but a big tender keeps you drier. We go long distances in ours and think nothing of doing a ten mile trip. Try that in a small deflatable and a 2.5hp. We also tow a wakeboard and go off to dive sites carrying all our dive gear for two people. All done comfortably on the plane. Our tender is a workhorse and a toy
lw395
Well-Known Member
I think 2T outboards have a broad spread of torque, because they don't have a motorbike-style tuned exhaust.
So they produce more power at e.g. half RPM than a 4T of the same HP, which will probably be a fairly revvy motor to get reasonable power to weight. A small 4T outboard is often prone to having the wrong prop to achieve optimum RPM, so it doesn't make its nominal power. 2T outboard can do the same, my little Yamaha won't rev enough to go fast on our big tender, but if you catch a wave it will rev up and hold the speed.
Monique
Well-Known Member
Probably the most important sentence in this thread.. especially if you live aboard.
Our 2 ST 15 HP Yammy is the dog's.....
greeny
Well-Known Member
Thanks for trying to explain. I still don't get it though as horsepower is a function of torque x revs / 5252. (thanks google).
So it it can't be different in a 2t to a 4t, or can it?
Or are the calculations done at a different rpm dependent on where the engine produces most torque. Therefore the quoted engine HP cannot be compared between 2t and 4t.