Humber 7m and 6cyl diesel

[Orkney1]

Humber 7m ocean extreme + Mercruiser VM4.2 230hp bravo 3 Tempted to try to make the two come together. I know what's involved, I'm just wondering am I going to make this thing far too stern heavy? If it would work I reckon I'll see 40 knots instead of 28. I already have a 300hp D-tronic in another boat. Seems a good engine .

Originally this had the 1.7 Merc grenade engine. That engine/ drive combination is 300kg. It now has a ford 2.5 engine, 300kg plus the alpha drive and transom gear so 400kg total maybe. The 4.2 with bravo 3 is 600kg

[beamishken]

Originally Posted by Orkney1

Humber 7m ocean extreme + Mercruiser VM4.2 230hp bravo 3 Tempted to try to make the two come together. I know what's involved, I'm just wondering am I going to make this thing far too stern heavy? If it would work I reckon I'll see 40 knots instead of 28. I already have a 300hp D-tronic in another boat. Seems a good engine .

Originally this had the 1.7 Merc grenade engine. That engine/ drive combination is 300kg. It now has a ford 2.5 engine, 300kg plus the alpha drive and transom gear so 400kg total maybe. The 4.2 with bravo 3 is 600kg

Depends on the hull type I guess my 7.4m delta did 39kts with a 240hp yamaha which is same weight as the merc you have. It isnt stern heavy but it's quite beemy & big diameter tubes assuming it's not a particularly narrow beam with skinny tubes it should be okay the 230 merc is a nice option, direct injection like the dtronic but no electronics. Much smoother and quieter than the 220hp indirect injection mercruiser engine it replaced

[Orkney1]

Originally Posted by beamishken

Depends on the hull type I guess my 7.4m delta did 39kts with a 240hp yamaha which is same weight as the merc you have. It isnt stern heavy but it's quite beemy & big diameter tubes assuming it's not a particularly narrow beam with skinny tubes it should be okay the 230 merc is a nice option, direct injection like the dtronic but no electronics. Much smoother and quieter than the 220hp indirect injection mercruiser engine it replaced

Yea I reckon your delta will be a fair bit wider than the Humber. It would be a bigger, heavier more robust boat overall would it?

[beamishken]

Originally Posted by Orkney1

Yea I reckon your delta will be a fair bit wider than the Humber. It would be a bigger, heavier more robust boat overall would it?

Yeh the delta is a heavy built boat but it also has a huge payload on the build plate, 2000kg iirc it's also plated for 370hp max power , I'm currently fitting a 315 yanmar what hp is the humber plated for? I dont think 230hp is particularly ott for a 7m boat. actually fitted a 220hp merc engine to a humber a few years ago for someone but cant remember exactly what size it was but I'm thinking it was maybe 6.5 or 6.8. The transom spec & hole cut out are the same for alpha drive & bravo drive so no problems there your probably adding 250kg in weight but its forward inside the boat not hung off the back like an overweight outboard I think it will be fine & a nice engine to have.
How does the boat handle now with a lot of weight in it? Your only adding roughly 3 big blokes into the boat

[Orkney1]

Originally Posted by beamishken

Yeh the delta is a heavy built boat but it also has a huge payload on the build plate, 2000kg iirc it's also plated for 370hp max power , I'm currently fitting a 315 yanmar what hp is the humber plated for? I dont think 230hp is particularly ott for a 7m boat. actually fitted a 220hp merc engine to a humber a few years ago for someone but cant remember exactly what size it was but I'm thinking it was maybe 6.5 or 6.8. The transom spec & hole cut out are the same for alpha drive & bravo drive so no problems there your probably adding 250kg in weight but its forward inside the boat not hung off the back like an overweight outboard I think it will be fine & a nice engine to have.
How does the boat handle now with a lot of weight in it? Your only adding roughly 3 big blokes into the boat

Looking at specs on Humber website it should be ok. 2000kg max payload. 225hp single/ 150hp.twin. max engine weight 500kg. And those will be figures for outboards I guess. At the moment I think it feels heavy in the stern, it was like that even with the 1.7. Maybe it's just the hull characteristics. On the plane it goes good but at transitioning speeds the thing just points at the sky, even trimmed right down. It's not a nice thing to be in if it's too rough to stay on plane. Trim tabs would likely help. Going for more power and bravo 3 drive would help in reducing the time to get out of the hole but then also it's adding weight. I have a 9.5m of unknown make, 300hp VM D-tronic. 11ft beam 3.6 ton. Only does 24 knots but it's a different animal altogether, you don't really notice it transition from displacement to planing, it just goes, doesn't feel like it's sitting in a hole pointing at the sky waiting for the turbo to spool up. Its doesn't accelerate quickly but it's very linear and predictable. The Humber is awful if you can't keep her on top due to sea conditions. Like if you can't do 16knts+ then you might as well only do 8knts. There is no inbetween. The big beast will sit happy at any speed. Dunno if it's a weight distribution thing or what it is. I think the fuel tank is also too far back on the Humber, probably doesn't help.

[beamishken]

I think it's just certain hull types have a different transition to plane, our hard boat cruiser is bad for it too, sticks its bow in the air till your past 20kts & you see many cruiser running like that but it feels awful. The delta doesnt do it either, it just stays flat like your bigger boat. The extra weight your adding might not make it much worse given your adding most of the weight inside the boat, moving the tank to compensate might be a big job & I'm not a fan of adding ballast up front to compensate but maybe worth trying some weight up front to see if moving the tank forward might help. I'd be interested to see how it gets on once its fitted

[Orkney1]

After some more measuring i think I'll stick with the ford engine and get it running reliably without overheating. Gonna take far too long cutting out a bigger hole in the deck and making a new engine box