what should i expect?

[markymarkP]

hi chaps,

i have just got the new rib, and want to take her out for a try dive on saturday.
i understand these things are a bit of trial and error, but wondered if i post up the specs, if anyone can give me an idea of what i should be able to expect:

she is
Bombard 6.2 mtr (SB620)
max weight 1600kg
unlaiden weight 400kg
115hp mercury 2stroke 20" prop
plated to take 12+skipper

so how many divers will she take, including all the kit etc, and what speed should she achieve when laden?

any help appreciated!

will know for sure on saturday!

[SeaSkills]

As you say, it's a bit trial-and-error. There is going to be a trade-off between load and performance, and my guess is that you're not going to carry many divers plus kit in a boat that size/weight with that size engine.

If you're not going far and you want to take a bigger group and don't mind taking longer getting to your dive site ... well, try it with 8 and see what happens

On the other hand, if your dive site is a little further away and you want to get there and back comfortably on the plane ... I'd be inclined to give it a go with maybe 4 to start with and see how you get on. With full kit you may need to get weight forward and full power to get onto the plane.

Bottom line is - I think you'll find you might be happier with a bigger engine to do the job you want (I'd be very pleased for you if I'm proved wrong)

Best of luck

Ian

[markymarkP]

Hmmm... i was going to try with 6 divers plus skipper on saturday, and see what happens!

[willk]

Try the six divers and their Paraphenalia. Put the load forward (along with the spare fuel ). I think you'll get somewhere in the mid-low 20s (kts)

[Poly]

Originally Posted by willk

Try the six divers and their Paraphenalia. Put the load forward (along with the spare fuel ). I think you'll get somewhere in the mid-low 20s (kts)

In which case is a 20" prop not massively oversized? I'd have thought something closer to 13-15" for those speeds ? And if I'm right then he may struggle to get on the plane when laden. Of course a 13" prop will rev the tits off the motor when unladen, so will need judicious use of the throttle or swapping props for the load on the day.

[markymarkP]

thanks guys, font of knowledge as always,

i will report back after saturday, and see what i get

will do as suggested


best

[Cookee]

Originally Posted by markymarkP

Bombard 6.2 mtr (SB620)

plated to take 12+skipper

They must have plated that on a particularly optimistic day!

[markymarkP]

here are the specs from them direct:

http://www.boat-finder.com/12518/details.php

[Poly]

Originally Posted by Cookee

They must have plated that on a particularly optimistic day!

It doesn't mean its designed to take 12 - just it won't sink if you do (and makes no promises about getting on the plane). Not quite as bad as Zodiac who put it in the product name...

[markymarkP]

well, i did wonder where they would all sit! even on the tubes, it seemed a lot!

i think my idea of about 6 is better. it has seats for 7.

suck it and see. i am not wanting to take loads, just interested in the possibilities

[Simon B]

12 passengers not divers! I would expect poor performance, though may be proved wrong. If it's a bit of flatter vee hull you may get enough speed. At a guess with 6 divers nad 2 crew I'd be looking much further down prop selection. Something along the lines of a 13" or 15"

It might be worth talking to Steel developments and thinking of a 4 blader, you'll see about 30 knots with divers flat calm but may over rev slightly when solo.

[markymarkP]

Thanks

We will be 6 divers and one crew,
I am keeping it as tight as i can!
We went out the other night, and were 6 on board, no dive gear, and got 30knots up to about half throttle.
if i can get everyone on, and gear, and get 20knots, i will be more than happy.

Normally we will be 4 divers and one crew. so this weekend, i am really testing her limits!

i hope to not have to change the prop, this one already on is brand new!

[willk]

hmmm, looking like I might be close. Keep a record of your speed/revs and report back

[Cookee]

Originally Posted by Polwart

It doesn't mean its designed to take 12 - just it won't sink if you do (and makes no promises about getting on the plane). Not quite as bad as Zodiac who put it in the product name...

Just shows what a load of steaming manure the CE regulations are - if you read the CE stuff it's meant to be the maximum designed load not how many you can cram on - it seems the Italian version lost a bit in the translation .....................................

[davej]

My BSAC branch has an excellent 5,5mtr Tornado with a yam 115 2S and with this we can just about get on board 8 divers and their kit, which then gets on the plane with about 23knts. However 6 is much more comfortable. I think from memory the prop on it is a Mich wheel 17 or 19" 3 blade.

good luck

[Simon B]

My experience of the performance of our Delta and 100hp Yam was although in good conditions it was ok it really did not take much to knock her off the plane then an eternity to climb back on to it in small swells. We just did not have the grunt to spin the prop up quickly so would lose momentum, hence the suggestion to look a bit lower in terms of pitch.

A 115 might bang out a touch more torque so may not be a problem, the Delta was a bit of a steep vee, this may not have helped us. Very good at going through waves though, still got a soft spot for Deltas.

[markymarkP]

ok, so you are dying to know!!
i took her out today, six divers plus skipper, dive gear for two dives, and.....


23 knots and 4600RPM

so i was quite happy with that!!

next time, i think 4 divers are sufficient, 6 it gets a bit crowded. maybe on short trips.

also, i burnt 46ltrs of fuel, on a 25mile round trip. we were motoring against the tide, in fair seas, up to force 4

[willk]

I'll post you that tenner now, shall I?