Opinions Please

[darklordhill]

Hi All
I am looking to power the 5.5m chinook I recently bought with only a small budget.
I can't decide on either twin 2 stroke 40s or a single 2 stroke 75.
Is the twin option going to be much more expensive to run ?
and is there a certain position they have to be in ?

[spartacus]

The old twins vs single engine debacle! Do a search on RIBnet, there's literally hours of reading material on this subject.

Regardless of budget, everything is more expensive with twins. You have added weight at stern, increased fuel, servicing costs, and rigging, if you include separate fuel filters which is essential.

For my money a 75hp engine is without question the best option. With the money you'll save, stick an auxilliary engine on for back-up.

[Harrys Game]

100 per cent agreement with Spartacus. Regards Jim

[Poly]

Twins have their place in the world, but you'd need a special reason to choose twin 40s on a smallish boat.

[darklordhill]

Originally Posted by Poly

Twins have their place in the world, but you'd need a special reason to choose twin 40s on a smallish boat.

Just because they look cool

But really I have the mind that if one should break down I have the benefit of the other as opposed to only having a small aux without the power to get me anywhere fast.

[Poly]

Originally Posted by darklordhill

Just because they look cool

But really I have the mind that if one should break down I have the benefit of the other as opposed to only having a small aux without the power to get me anywhere fast.

To actually get this benefit you need 2 totally different electrical and fuel systems. Carefully selected with just this purpose in mind one 40 HP will get you home - but badly planned it will have the wrong prop and struggle.

If you use your boat in situations where twins makes sense and the cost and performance disadvantages etc are outweighed then you probably wouldn't be asking.

[darklordhill]

Separate fuel and elec No problem
Carefully selected prop will be trial and error I guess.
The situations I plan on putting this boat into are more adventurous than I have been in the past.
I want to do a trip to the scilly isles and if that goes well a channel crossing.
I have gone further in distance but always hugged the coast.

The twin idea is like a crotch, it is supposed to make me feel safer.

[Poly]

Originally Posted by darklordhill

The twin idea is like a crotch,

aye its certainly not far away

it is supposed to make me feel safer.

Look up "risk compensation"

if you want it - do it - but its not the approach 90% of people here would take. Service engines well, know how to trouble shoot and fix minor/common issues, keep a close eye on performance indicators / warnings, a decent sized aux, cruising in company, investing in better comms kit. Having 2 engines is no certainty that you won't run into a problem.

Whilst I wouldn't want to be stranded mid channel you are actually in an area with (1) lots of shipping (2) pretty reasonable comms (3) good rescue coverage - and in a 5.5m boat you presumably would only be attempting it in pretty good conditions.

If the boat has not been rigged for twins before you may have some work to do - and it may not be trivial (e.g. involving irreversible angle grinding!).

[darklordhill]

" Risk compensation is a theory which suggests that people typically adjust their behavior in response to the perceived level of risk, becoming more careful where they sense greater risk and less careful if they feel more protected. Although usually small in comparison to the fundamental benefits of safety interventions, it may result in a lower net benefit than expected. "

That is so true.

Well serviced and in the best condition I can get them.
Being a mechanic the troubleshooting and fixing is no problem along as I have the right tools at hand, i.e Duct tape,wd40 and cable ties.
Crossing in company would be great but I have no friends with boats.

I think its probably not the worst place to be stranded but trying to make head way with a little aux is not the way I want to go, and yes I only plan on crossing on the finest of days.

Maybe I should be looking for a decent size aux that has enough power to push me along at decent rate but at the same time be light enough not to hamper performance.

[Pikey Dave]

Bear in mind that this is coming from a bloke with a twin engine boat (for sale) & who has a single engine boat on order:-


Twin engine, I specced this as a dive boat, the rationale being that we were diving 20+ miles off shore, deep stuff. If I put divers in the water, I wanted to be sure that I could get them out again, especially if they've been drifting a couple of hours doing deco. The boat has completely separate fuel & electrical systems for each engine, it will plane on one engine, the fuel tanks can be combined to a) run both engines from 1 tank, or b) 1 engine from both tanks. This means that the loss of 1 engine or 1 fuel tank doesn't mean you lose the corresponding engine/fuel. Similarly, the batteries can be combined to run/start/charge from any engine.
I've even gone as far as having separate plotters/gps so that failure of one unit doesn't mean the loss of the whole system, paranoid moi???


New boat:- Single engine, smaller boat. I've stopped diving & now don't need anywhere the level of redundancy. We still do the distances, but usually in company. We are well equipped with drysuits/plb/290N lifejackets yada yada! If it all goes brown, the worst that happens is we drift/anchor & wait for the cavalry.


Twins are undoubtedly more expensive to buy/own/keep. In your case twin 40s will nowhere perform as well as a single 75 of similar pedigree. Unless you have under deck tanks, you will have fuel cans all over the place gobbling up valuable deck space.


At the end of the day, it's your call. You did ask

[Poly]

Originally Posted by darklordhill

Crossing in company would be great but I have no friends with boats.

you've got 18,429 of them you've just not met them yet!

Maybe I should be looking for a decent size aux that has enough power to push me along at decent rate but at the same time be light enough not to hamper performance.

the usual rule of thumb quoted is 1HP per m of length - so 6HP for you - but if it would fit a 9.9 might make good progress on your boat (plenty of yachts your size will have sailed the channel with engines that scale).

[darklordhill]

I have been looking for a small aux around a 9-10hp, but the next consideration is getting the right weight / balance with whatever main I get. I think I need to see more of other peoples setups with the same size boat.

[darklordhill]

Originally Posted by Pikey Dave

Bear in mind that this is coming from a bloke with a twin engine boat (for sale) & who has a single engine boat on order:-


Twin engine, I specced this as a dive boat, the rationale being that we were diving 20+ miles off shore, deep stuff. If I put divers in the water, I wanted to be sure that I could get them out again, especially if they've been drifting a couple of hours doing deco. The boat has completely separate fuel & electrical systems for each engine, it will plane on one engine, the fuel tanks can be combined to a) run both engines from 1 tank, or b) 1 engine from both tanks. This means that the loss of 1 engine or 1 fuel tank doesn't mean you lose the corresponding engine/fuel. Similarly, the batteries can be combined to run/start/charge from any engine.
I've even gone as far as having separate plotters/gps so that failure of one unit doesn't mean the loss of the whole system, paranoid moi???


New boat:- Single engine, smaller boat. I've stopped diving & now don't need anywhere the level of redundancy. We still do the distances, but usually in company. We are well equipped with drysuits/plb/290N lifejackets yada yada! If it all goes brown, the worst that happens is we drift/anchor & wait for the cavalry.


Twins are undoubtedly more expensive to buy/own/keep. In your case twin 40s will nowhere perform as well as a single 75 of similar pedigree. Unless you have under deck tanks, you will have fuel cans all over the place gobbling up valuable deck space.


At the end of the day, it's your call. You did ask

I guess that the twins you have are big as only one has enough power to get the boat planing.

I think that the with the small twin 40s I was contemplating one would not get the boat planing if the other went down, so a decent aux may do just as well.

I may just steer toward the single 2 stroke 75 with an aux or I may put it off for while and save to get the super light 4 stroke yam f70 that I keep reading about, Just can't seem to find any cheap used ones.

[Last Tango]

The weight of two 40s is significant, with the 100+ litres of fuel you'll need to feed them, will it push the weight of the boat/trailer over 750KG...braked trailer needed? Probably less than 1 kn/ltr...range issues?
If you're buying second hand then you're money is better spent on one good 75hp rather than two more "iffy" 40hps. Then again if you don't spend the money wisely on engines your wife will probably waste it on something stupid like a new kitchen or shoes.......

[darklordhill]

Originally Posted by Last Tango

Then again if you don't spend the money wisely on engines your wife will probably waste it on something stupid like a new kitchen or shoes.......

Ah you no her indoors then, She has just had a new kitchen before Christmas and funnily enough new boots for christmas.

I think if I make a start on the extension she will be pleased with me and I could secretly syphon of enough for a new outboard

[spartacus]

Originally Posted by darklordhill

I may just steer toward the single 2 stroke 75 with an aux or I may put it off for while and save to get the super light 4 stroke yam f70 that I keep reading about, Just can't seem to find any cheap used ones.

The F70 is a fantastic engine, but if you're looking for one second-hand you'd be better off digging out a Damart catalogue and ordering your pipe and slippers now.

Its only been on the market since 2010, so I seriously doubt there's sufficent volume in the market for them to start appearing quite yet. I looked for a set of second hand Yammie 50G carbs for 2 years before giving up the hunt.

Second-hand Yammie 75hp here: Buy Used Outboards yamaha 75hp 2007 model 2 stroke, power trim, 250hrs from new 75.0HP Outboard at Bill Higham Marine

[darklordhill]

Originally Posted by spartacus

I looked for a set of second hand Yammie 50G carbs for 2 years before giving up the hunt. [/url]

I did the same with carbs for a honda 90, A set turned up within weeks of selling the engine. Never say never.

That Yammie looks good, I did not know they were making them in 2007.

[spartacus]

Looks like ex-RNLI. Decals on the leg, capsize solenoid on engine tray, etc.

[Seafox47]

You know i always believe in redundancy and specifically purchased a RIB (nautica 680) with twin outboards. I do cross Lake Ontario quite often in the summer and the added safety it provides is a comfort level i could not do without. Having said that i never had a failure on either engine ever and the key lies in proper maintenance of the equipment.
Regardless of what you decide, keep in mind that the performance with twin 40 in your case will be nowhere near the performance of a single 75. I believe you need twin 50 to get similar performance the single 75 will provide.
As your rib is a 550 a small aux engine of around 10 hp would give you the comfort level and when you maintain the 75 properly, you probably never have to use the 10 hp