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Old 03 October 2006, 17:54   #1
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Re-engine or go for twin-engines

Dear all,

I'm close to finishing my first season ribbing, and I've covered best part of a 1000 miles this year, which is more than the previous 6 years sailing.

My rib is an 8.5m Scorpion with a 225 Opti. Both have been fantastic apart from the odd glitch with the Opti (2001, 500 hrs). I've progressively pushed my comfort zone, and now often out in F5+, which is fine, but not great if your engine goes. So I think I've got two options:

1. Re-engine with a Suzuki 300, add dual fuel filters, spare tank, and separate battery/electric install. In my (limited) experience, I reckon it's usually fuel or power that stops boats.
2. Go all out for a new or nearly new twin engined Scorpion.

Downside for no.2 is it's a lot of cash, both upfront, and in terms of running costs.

What do you wise ribbers think?

Atb,


Phil
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Old 03 October 2006, 17:57   #2
pop
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why not put twins on yours
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Old 03 October 2006, 21:41   #3
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If I had the money (highly unlikely) I'd love something with a decent set of twins on it both for the safety factor but also the pure appeal of lots of engines

One engine is still one engine if it stops...
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Old 03 October 2006, 22:29   #4
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I am in a very similar dilemma with my boat - I really love my suzuki DT225 - it's awesome but my hull is just crying out for more power. I really don't want to go for 2x engines. The extra cost and extra fuel are one thing but also the extra weight hanging off the transom will spoil the balance. My boat lands nice and level off big waves unlike most of the twins I have seen.

I already have 2x everything on fuel and 2x batteries - also an aux 15hp(not fitted yet). I WAS looking at the Suzuki 300hp 4 stroke but now something else has taken my fancy - the new Mercury racing 300xs. It is a good old 2 stroke but with Optimax technology - even better it is very light - only 225kgs!!!
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Old 04 October 2006, 02:53   #5
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Quote:
Originally Posted by codprawn
....also the extra weight hanging off the transom will spoil the balance. My boat lands nice and level off big waves unlike most of the twins I have seen.
My boat flies and lands nicely, my console is quite far forward, which helps. But the back of the boat coming down first isn't always a bad thing - less chance of landing nose into a wave.

You can sort balance by adding ballast in the bow... so I don't think balance is neccessarily a good reason not to go for a twin setup.

If I was planning on taking the boat out in rough weather a lot, there is no doubt in my mind that I'd go for twins. I believe an auxillary is pointless in bad weather - unless its a decent size, it probably wont push you against the wind and tide, and if it does - it would be an extremely long ride home.

With my twin engine setup now (twin 150hp Yamaha HPDI) and the 7.5m Tornado, I get about 53-54 knots top speed. The hole shot is extrememly good, it pops out of the water onto the plain in a couple of seconds and is off ... probably up to about 40 knots in 5-7 seconds (I haven't timed it, but its bloody fast!). I have tested the boat with a single engine, with the other tilted up, and I get 30 knots - which is a very good "get me home" speed.

Theres a couple of downsides to twin engines - two lots of maintenance costs, and a larger fuel consumption - which might mean increasing the size of the tanks on your boat. I currently have 180litres of fuel (in two 90litre tanks)... which will in theory of me doing 60l/h at about 40 knots, will get me 120nm which isnt a bad range, but I want more.
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Old 04 October 2006, 06:06   #6
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Quote:
Originally Posted by benc
If I was planning on taking the boat out in rough weather a lot, there is no doubt in my mind that I'd go for twins. I believe an auxillary is pointless in bad weather - unless its a decent size, it probably wont push you against the wind and tide, and if it does - it would be an extremely long ride home.
That's sort of my feeling because the Law of Sod indicates the main fan will stop at the worst possible moment (bit like the same law applied to a single engined aeroplane which indicates it will stop over water....).

I don't know much about balancing a boat when its airborne but like most things I think you can see when it's been done right. The video link somebody posted of a Zodiac CZ7 a few days back was awesome, I couldn't believe the way that thing just whistled across a rolling swell with literally just the props in the water for half the time, every landing was perfect, the balance to do that must have been perfect, and it had twins. If I ever get an obscene amount of money from anywhere I am going to buy one of those. No question
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Old 04 October 2006, 07:33   #7
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Look again - a few of the landings were fairly stern end heavy. I know I watched that video about 100 times!!!

If you thought that was impressive watch this

http://www.boomeranger.fi/images/ind...conditions.mpg

Right at the start you will see the boat lands VERY stern down - but it is running unladen - all the seats in the front would normally be filled with troops which would balance it out far better.

It is only at the very end when it comes alongside the support vessel you realise just how rough it REALLY is!!!

Impressive holeshot isn't only the preserve of twins - my boat jumps like a scalded cat because of the 19" 4 blade prop - limits my top speed to 41kts thopugh - will try another prop this weekend....
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Old 04 October 2006, 07:45   #8
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Quote:
Originally Posted by codprawn
Impressive holeshot isn't only the preserve of twins - my boat jumps like a scalded cat because of the 19" 4 blade prop - limits my top speed to 41kts thopugh - will try another prop this weekend....
I'd like to see it against mine

You should come venture out in the solent sometime
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Old 04 October 2006, 08:13   #9
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Quote:
Originally Posted by benc
I'd like to see it against mine

You should come venture out in the solent sometime

Can't stand those horrible little waves - much prefer a big rolling Atlantic swell.
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Old 04 October 2006, 09:13   #10
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Re: twins

Consider this: if you have two additional passengers seated in the aft of your boat, that could probably equal the weight of a additional motor. I feel a twin engine boat cuts/pushes through the waves better due to the extra prop (more bite). I don't notice the extra weight in the stern affecting the attitude or performance of the boat negatively, and I think the boat pitches less port to starboard underway due to two props driving it. In a boat 8 meters or greater in length you probably won't negatively affect its ride by adding another motor, (making it stern heavy). If you are thinking about switching to twins an outboard bracket makes a lot of sense, it gives you a full height transom, (no motor cutout) the motors can be trimmed all the way out of the water, it adds additional bouyancy to the stern of the boat, and it adds length to the hull, this benefits twin and single engined boats. I don't see brackets on U.K. based ribs, not sure why this is so as brackets are a very common feature on boats here in the states, they work well!
I would think someone could make a lot of money building and selling outboard brackets to the market over there, just a thought...
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