Currently have a 6.4m Tornado with twin merc 90hp 2 strokes. They run fine and it's nice having the (potential) redundancy. Have got an opportunity to switch to a single 150hp 4 stroke which should significantly reduce fuel usage and move to a modern, quiet engine better at idling during diving.
I've been through and thought of all the potential changes that might be needed but I'm sure I've missed some. Would appreciate thoughts from anyone who has done the same/got some pearls of wisdom.
- Need to check the XL shaft length is ok for single motor as currently the twins are L but offset away from the base of the hull.
- Dual fuel tank and filter set up currently would need 3 way tap. Could use two (one at tank end and one at engine end) to be able to still swap to a second filter. Would need to remember to swap it every so often to balance boat.
- Dual battery setup currently but separate so could add ACR between the two.
- Hydraulic steering operates on port engine and then tie bar to starboard. Can hopefully swap this to new engine but need to check ram mounts arent stuck in current OBs.
- Trunk is currently central between the two engines so would need to block up and cut new one to the side. Assuming transom is solid there will still be enough structure there.
- Engine bolts holes to be infilled with epoxy and patched.
- Might need to budget for an aux to be able to pickup divers in event of a breakdown. Got a standard shaft 15hp for SIB but may not be practical.
If your boat was built for twins the transom may be set up for them. Is there knees to support each engine? Just a nudge to think about the forces on your transom shifting. Your manufacturer would know best [emoji4]
I have a tornado 6.5m and have known the rib since new (1996 manufacture I know own her ) and she has had a Yamaha 115hp Mercury optmax 150 hp (both 2 strokes and she now has a Suzuki DF 150 HP four stroke plenty powerful enough and the boat never had twin engines
if that helps
If your boat was built for twins the transom may be set up for them. Is there knees to support each engine? Just a nudge to think about the forces on your transom shifting. Your manufacturer would know best [emoji4]
That’s a very good thought thanks. Just had a search around google images and all the 6.4s I can find seem to have to same transom knee arrangement as mine. Lots with single engine setup so looks as if the hull was universal.
I have a tornado 6.5m and have known the rib since new (1996 manufacture I know own her ) and she has had a Yamaha 115hp Mercury optmax 150 hp (both 2 strokes and she now has a Suzuki DF 150 HP four stroke plenty powerful enough and the boat never had twin engines
if that helps
That’s good to know, thanks. Would be very interested to know the sort of performance and economy you are getting from the DF150. Bare the boat weighs 1200kgs (including 250 litres of fuel) and out max payload is about another tonne (6 divers with technical kit) so we would be quite heavy. Probably would need quite a coarse prop. What shaft length engine are you running?
6.4 with a 150 optimax and 5 aux 160L fuel tank twin consol, we run with 6 divers no problem, we really need to change the prop from the standard laser 2 19p as we can’t get max revs but haven’t had the cash to try any others,
That’s good to know, thanks. Would be very interested to know the sort of performance and economy you are getting from the DF150. Bare the boat weighs 1200kgs (including 250 litres of fuel) and out max payload is about another tonne (6 divers with technical kit) so we would be quite heavy. Probably would need quite a coarse prop. What shaft length engine are you running?
I can get 32 -38 knots depending on sea state with 4 people on board . The boat is away in storage so I can't measure the shaft length but the number is Suzuki DF 150 15002F-111669 if it helps . We once weighed the boat and trailer on a public weigh bridge at 1300kg with 120 litre tank
