Too much power?

Will F · 07 December 2005, 17:14

I'm buying a Humber 5.5m Ocean Pro and I'm waivering over which engine I should get. My previous boat was a 5.4m Tornado with a Yamaha 90 2-stroke. She had alot of difficulty getting on the plane with 6 divers and a coxswain so I'm keen to avoid a similar problem this time. Just to make things interesting, I'm also fairly tightly constrained by weight because I'll be towing with a normal family car, so the lighter the better and 4-strokes are right-out. At the moment I've pretty much made up my mind on a 115HP Evinrude E-tec, which is 50Kg heavier than the Yamaha 90 but I think necessary none the less. Does anyone have a similar boat, what engine did you go for? Is the 115HP overkill? Or does anyone have any recommendations either way?

bogib · 07 December 2005, 17:22

What about Mercury / Mariner 115 Optimax, weight about 170 kgs

Bogi

Hugh Jardon · 07 December 2005, 17:25

ask the dealer if they can supply a 2005 engine for you at a discounted price, ie for merc or mariner that is....

if the boat is rated for 115 then you have no problems, always better to go bigger than smaller if the car towing situation will allow

if the boat can take a bigger engine and the bigger engine is the same weight as the 115 then go bigger

Quote:

Originally Posted by Will F

I'm buying a Humber 5.5m Ocean Pro and I'm waivering over which engine I should get. My previous boat was a 5.4m Tornado with a Yamaha 90 2-stroke. She had alot of difficulty getting on the plane with 6 divers and a coxswain so I'm keen to avoid a similar problem this time. Just to make things interesting, I'm also fairly tightly constrained by weight because I'll be towing with a normal family car, so the lighter the better and 4-strokes are right-out. At the moment I've pretty much made up my mind on a 115HP Evinrude E-tec, which is 50Kg heavier than the Yamaha 90 but I think necessary none the less. Does anyone have a similar boat, what engine did you go for? Is the 115HP overkill? Or does anyone have any recommendations either way?

jyasaki · 07 December 2005, 18:46

If I were you, I'd find what the hull is rated for, and make your decision on which motor based on that.

As a fellow diver, I am well aware of the amount of weight a boat loaded with gear and divers (and, on the trip back, water) has to deal with; go max power and you won't have to second-guess your purchase.

Given that you will be adding a ton (literally) of weight in the passenger area, a few more pounds in back is not going to matter all that much, I think.

jky

jwalker · 07 December 2005, 22:56

Some folk on ribnet rate the Suzi 140. That would give you the extra oomph for carrying your gear.

roycruse · 07 December 2005, 23:14

Quote:

Originally Posted by jwalker

Some folk on ribnet rate the Suzi 140. That would give you the extra oomph for carrying your gear.

I have one - on my ribcraft 5.85 - love it.

You also have to remember its lighter than ther suzuki 90hp

thorper · 08 December 2005, 10:12

For getting the rib on the plane loaded with divers, its the torque / pickup you want rather than raw power at the top end. You defnintely want a 2 stroke for pushing load around at that size.

The prop you pick for carrying load is important as well - worth discussing with the dealer when you buy the boat.

Our club dive rib (6m) has an Optimax 115, which pushes 6 divers + a cox up on the plane without too much bother, and it is a good engine too.

Ricky

Surferdude · 08 December 2005, 19:38

You can also change the prop to one that lets you get to a plane faster. That might save you a lot of money.

Hugh Jardon · 08 December 2005, 21:07

and try doel fins on the prop, they work wonders in certain situations

Dirk Diggler · 08 December 2005, 21:36

Quote:

Originally Posted by Hugh Jardon

and try doel fins on the prop, they work wonders in certain situations

Can't imagine what situation that would be, might be worth trying them on the cav plate though!

Hugh Jardon · 08 December 2005, 21:50

now that would be a sight to see

yes cavitation plate it is, oooops what a birk!! playing with my new laptop here so brain not totally engaged

Quote:

Originally Posted by Dirk Diggler

Can't imagine what situation that would be, might be worth trying them on the cav plate though!

Fjordrafting · 09 December 2005, 11:08

We used to have a 5.5 Bombard rated for 90 hp. We had 115 Johnson 2-stroke. It did 42 knots on GPS when two persons on board. This was the speed we wanted for cruisingspeed. We always wanted more hp and looked at 150hp so that we could cruise at 40+ knots.
Ask the builder if the transom can hold the extra hp, so you don`t break anything. When bying a new boat, you can specify the transom yourself.

Simon B · 09 December 2005, 13:02

Will F,

Our club currently runs a Delta 5.5 with a Yam 100 hp 4 stroke. We wanted the F115A but didnt have the money. Its a heavy motor and we pay for this due to the whole thing being stern heavy. We also used the the Yam stock prop which was well out in terms of pitch for the speed we needed and ability to plane with 6 divers and 2 crew.

The biggest difference to date has been going down in pitch and using a 4 blade prop. We particularly noticed this when you are just off the plane and climbing the front of a wave, previously it was like slowly driving into treacle.

We will be fitting lifting foils but I'd like to wait until some new stock of "Tigershark" Vortex groove foils arrive and try them.