what motor for a 6 meter alloy boat?

[spearking]

My father in law is looking at buying a custom built plate alloy boat, being custom there is no Hp recommendations. The boat currently has a 98 model mercury 150 blackmax 2 stroke, he is thinking about upgrading to a new 07 model 115 mercury optimax, would anyone think this is in the ball park?

[Show me the fish]

I am currently looking into getting a similar size boat. The 6m plate boat i am looking at has a recommended HP range of 130 - 150. I am currently leaning towards a 140 Sukuzi 4 stroke.

[Malcolm W]

I suppose it depends on what you do or want from it(father in law, I gather he probably wont be a rev head). I have a similar size plate boat with a 115 2 stroke and its more than adequate, 33knts flat and 22knts @ 4000 rpm. 3 divers 6 tanks and full of fuel does not seem to bog it down too much.

There may be the odd occasion when you need more power but the opti 115 is a pretty good all round package for that size boat (dealer, price and economy). I think it should do the job well, but I wouldn't go any lower

[FNQCairns]

personally i wouldn't choose that engine on that boat, it would probably work (just, but not really) as a fishing rig when light but once setup for offshore with all of the typical trimmings it will struggle, that opti is only a 3cylinder, IMO go with a 4cylinder for the torque advantage, the 135 opti would make a good fishing rig out of it or any of the larger 4 cylinder 4strokes.

The 3cyl opti simply will not pull the prop pitch needed to make it a workable fishing rig but it will high cruise at 20-22kn but because of the low prop pitch needed and with a typical 6m hulls need to travel at near 25kn to start to become efficient it will always be a bit of a mess.

cheers fnq

[robothefisho]

A tad on the low side but perfectly adequate for 2 people to go fishing, depending on the weight of the boat, anything under 850kg hull only should be ok. Ifit was regularly loaded with 4 blokes eskies 300l fuel etc imho would definately need more grunt.

[Luke G]

Go for the max HP, there is a big difference between a 140 Suzuki and 150.

[rosco1974]

i would put a 150 on it ,have a 610 plate with a 140,cruises at 25knots at 4500 and wot just under 35 knots

[indy]

Go the 150 you will always want that little extra i have a 140 suzuki four stroke on a 6m and wish there was a 150 on the back for those clean days.

[Skusto]

how heavy is it? a 115 would be boderline depends on the intended use. we got a 150 on a 560 and love it uses just a little bit more fuel then the old 115 but not much and works not as hard.

[wrxhoon]

115 Would be to small for my liking , I would go for the 150 opti because the 135 opti is a V6 and the same weight as the 150.
By having the bigger angine you don't need to run it flat out and when she is fully loaded she will strugle with the 115.

[screaming reels]

G,day spearking, just going to add my two bobs worth, firstly a boat should be balance between hull and motor e.g if overpowered the motor will steer the boat if underpowered the boat will steer the motor, right balance is key,second is if doing a lot of ocean running YOU need slightly more horses for bar crossings and for those long trips back home when punching through big seas the last thing you need in those situations is to be underpowered. Look i would go the 150 hp you will find performance all round will be greatly improved e.g good mate 6m sportfish upgraded old johno to a 150hp standard 2 banger(new) his boat is heaps better doeesn"t labour on the back of swells touch the throtle and up and over. hope this helps cheers Brent

[spearking]

Thanks for everyones advice... the post help me confirm my suggestions to the in laws, I will pass on the helpful info
regards to all

[revs57]

One quick comment, I had a 150 efi (non opti) on my 6mt Riptide (read 6.6 loa) for around 150 hrs. The best fuel return was 33-35 lts per hour at 3800 RPM pulling a 19" prop - it pulled up a little short on WOT but it was a bit thirsty - give it a bit of a work out and you could almost see the fuel gauge dropping. I know another fella who put a 140 carb V6 merc on his 6mt riptide, he got better performance out of that than I did the 150 efi.

I upgraded to a F200 Yam 4stroke and have never looked back - 18lts /hr or 1lt to 1 nautical mile, plenty of torque and excellent response for crossing bars around SE Qld. So glad I went the extra - I'd be thinking on a 6mt platey you'd need at least a V6 something, even the 140 'zuke, and they are an excellent motor, would be a little stretched IMO for the kind of offshore work I do.

cheers
Rhys