Originally Posted by Poly
Changing from single to twins isn't trivial and the benefits may be less than you expect. Not all transoms would take the weight or power of two big engines either.
Originally Posted by ShinyShoe
TwinsAs Poly said twins is not the sensible option. 2 x70HP would give you power something like 100HP...
..... If an engine fails you either have a 6HP spare to deploy or you chuck out the anchor and hope some nice passing boat gives you a tow.
Jepho, Hi, Welcome to ribnet!
There is a lot of banter around single vs twins. I'll summarise here by saying what is maybe true with twin 150s vs a 300 is not necessarily true lower down the scale. Poly's comment on changing from singe to twins is spot on - as you will need to rebuild the transom. Twins to singe usually involves removing wood.
Do a search for twin - single and filter for me in the user box - I have expanded on these misconseptions numerous times, but in summary:
- at the bigger engines due to the lower sales volumes more share the same hardware so quite often a 150 will be not too far off the weight of a 300. Down at the "100 or so" mark quite often twins can weigh less than a single + aux. Search my other posts for some real life examples.
- Most older engines once running are entirely self sufficent. Also most new engines with a tiller option likewise - others you'll need to check, E.g my (admittedlty very old) clamshell I could disconnect the battetry and it would still run. Plenty of threads on here about emergency pull starting.....
- nope. The drag is approx related to the frontal area cubed & the speed squared. smaller engines have smaller gearboxes, and the smaller the boat the less the top speed is likely to be, and as most on here regardless of boat or engine size reckon about 1l/nautical mile at 20-25 knots cruising speed..... (look for the fuel economy threads)
Originally Posted by jepho
Thanks Poly. Is there a particular type of transom I would need to ensure was in the specification? I have no idea what to ask for.
Will it be obvious which hulls would permit two engines?
Please forgive the dumb questions.
There is no such thing as a dumb question.... someone will always know more on a subject. you may be answering smeone else's Q next time.
Transoms these days are usually rated for a weight and a HP. Some show a separate set of numbers for twins. Simple rule - don't exceed those numbers!
Re. the transom for twins - most transoms will need a "well" cut in for a single. This is because there is less transom depth the further from the centreline ine you go so the prop then hangs below it and so don't need to cut the transom. I seriously looked at twin 30s for mine, as I had a helathy 30 from my previous SR4 but as the Humber's transom was cut the woodwork was going to be way too much hassle so I got a single 60 instesad.
Also re,. the "underpowered" thing - most on here would say "go as big as you can" - to which I agree, BUT if your budget doesn't allow then "underpowered" isn't the end of the world.
E.G. most here would say "get a 50 - absolute minmum a 40" for a 4m Searider......errrr I ran one with a 25Hp for 3 years, and it crusied at 20 knots quite happily. Ok, took a few seconds to get up on the plane as opposed to "instant", but unless you are stop - start rescue boat type work is that really an issue? - Upgrading to a bigger engine later is always an option.
Another thing to think of - as we have all done you buy what you think is the baot you want...until you use it and realise that actually this would have been bettrr if... and that isn't really needed for my use..... type thing. Chances are you will be changing for something new (to you!) in a few years anyway.
Whatever happens there will be plenty of opinion to weigh up on here! ....and whahtever happens - your choice will suit your way of working / budget / travel / etc.