Gemini Military Spec SIB

Slaphead · 03 March 2008, 20:59

Hi, I've just bought one of these from JBT and I'm going to pick it up in England tomorrow.
I intend to use it for servicing my moorings in Strangford Lough with 2 divers max and maybe one to provide top cover in the sib.
My questions are- I want to use a two stroke tiller steer to power it but what size,25 or 40hp?
Short Shaft or Long?
I also want to do a bit of blasting about with my wife and 5 year old son in the relatively tranquil waters of the lough.
The whole lot comes home in a car trailer aftrerwards.
As I value your expertise, what would you use?

martini · 03 March 2008, 21:09

You mean these?

My guess is a 40hp short shaft would be ideal.

Slaphead · 03 March 2008, 21:17

Yep, that's the one. What sort of weight would be in a 40. I'm talking of removing from boat, into trailer, out of trailer, then into wheelie bin to flush, etc... I'm reasonably fit but would I end up with arms like popeye?
Other question. Apparently it's 80kg. Would transom wheels be a good idea?

martini · 03 March 2008, 21:45

You might be better off with a more suitable sib trailer where you can keep the engine on the boat and run it up with muffs on

MustRib · 03 March 2008, 22:50

I really dont think you will lift a 40 hp OB by yourself.
25 hp is about the limit to avoid injury....
The 20hp 2 stroke Yam on my SIB is about my realistic limit without damaging myself or the motor....whilst still being "portable".

Just wait a second though and someone else will be along with
some little known variation of a propriety outboard that weighs less than
a bag of sugar and produces 50hp

Locozodiac · 03 March 2008, 23:59

Yes, plainly agree with MustRib 25/30 HP 2 strokes (52 KG) will be the max to carry in short displacements to avoid injury and pain, 2 buddies will do the job better, as you get older and so your skelleton will only want to carry 5 HP engines...

Will be just fine with a sib trailer to keep engine placed at all the time, have been placing & removing engines on/off sibs for years and now that have a nice trailer my spine is very happy, has found a new transporting mate, highly recommended, a must issue.

Andy Gee · 04 March 2008, 07:38

Quote:

Originally Posted by Slaphead

Hi, I've just bought one of these from JBT and I'm going to pick it up in England tomorrow.
I intend to use it for servicing my moorings in Strangford Lough with 2 divers max and maybe one to provide top cover in the sib.
My questions are- I want to use a two stroke tiller steer to power it but what size,25 or 40hp?
Short Shaft or Long?
I also want to do a bit of blasting about with my wife and 5 year old son in the relatively tranquil waters of the lough.
The whole lot comes home in a car trailer aftrerwards.
As I value your expertise, what would you use?

We used to use one similar to this for ferrying divers about inshore. It originally had a 28hp Yamaha on it and went very well. Later we used it inland with a 8hp short shaft Yammie for ferrying kit about and it was okay,but very slow and the engine would usually over heat!! I would'nt want to go into tidal water-especially Strangford with anything less that about a 25hp and a 40hp you could have some serious fun.
I would get a basic launching trailer for it and just launch/recover from a slip with a 40hp.
Andy

Slaphead · 04 March 2008, 22:16

Unfortunately I don't have room for another boat trailer at the house so it has to be the car trailer option. I'll maybe just stick with a 25.
Thank you all.

John Kennett · 05 March 2008, 09:03

Quote:

Originally Posted by Slaphead

I'll maybe just stick with a 25.

I'd agree with that. A 25hp 2-stroke is the largest motor I'd want to carry anywhere.

John

prairie tuber · 05 March 2008, 12:46

How long is this boat - 4.2m?, 4.7m? What fabric is it made of?

If it is 'military spec' I would imagine that is boat is made of hypalon (maybe 1100 dtx, but more likely 1670 dtx) rather than PVC. If the boat is 4.2m & 1100 dtx hypalon, it's weight will be alot will be closer to 110 than 80 kg. If it is 4.7m and/or the heavier hypalon it will weigh alot more than that.

I could be wrong about this but the '80kg' is might be transom & fabric only, and not accounting for the floorboards.

Even if it comes in at 80kg, floorboards included, launching wheels will be an absolute must if you aren't going to be launching it directly from a trailer.

prairie tuber · 05 March 2008, 13:01

Couple more things to consider;

First off what is the max power this boat is rated for? If it is a 4.2m boat, it is probably 40hp, if 4.7m, probably closer to 60hp.

A 25hp 2-stroke will weigh somewhere around 45-52kg. A 40hp or 50hp 2-stroke will weigh somewhere from 70-80kg. If the weight of the fabric/transom unit is in the ballpark of what I suspect it to be, your going to need a way of hauling/hoisting/maneuvering/storing a fabric & transom unit that weighs as much as a 40/50hp 2 stroke.

Slaphead · 05 March 2008, 14:22

You're right about the weight.
JBT told me 80kg.
There is no way that sib is 80kg. When I collected her yesterday it was in two packages on a pallet, one being the fabric and one I think the floorboards.
Two men could just about lift each one and set it into the small boat I also bought.
The fabric is hypalon and I would estimate at least 120kg...ish all up.

As an aside issue, I purchased separately a 15hp Yam short shaft for the small boat but the transom is about 3" too deep so I'll just use the Yam on the Gemini in the meantime. It should be powerful enough to push me around against the tides as it's main use will be to service moorings at slack water.

Boat is 4.5m

prairie tuber · 05 March 2008, 14:33

That boat should hold up to alot of very heavy useage. It certainly isn't your garden variety SIB designed to fit in a car trunk (boot). I'd bet that the transom thickness is near double what you'd see on most SIBs.

Searider · 05 March 2008, 15:03

The Navy have these Geminis on the back of their P2000 patrol craft. These have a 20hp Mariner 2 stroke with prop guards. Fairly sluggish with 3 or more persons on board - but probably due to the prop guards as much as anything.

When I was a student and in the RNR we had the same / similar Geminis with 35hp 2 stroke Evinrudes. They flew with those! Bit of a handful mind.

Slaphead · 06 March 2008, 18:56

I took the bathroom scales and weighed the various bits which make up the sib. The three packages in the first pic from top to bottom are the keel section, the floor and the fabric of the boat.
30kg, 60kg and 60kg respectively.
As there are no instructions with the sib I hadn't a clue what the items were in pic 2 but Jason at JBT told me they are the sections that make up the keel... thanks for that.
The next pic shows the fold up floor which is incredibly heavy. The green bit of wood with the groove cut out I think is part of the rear section of floor where it meets the transom.
Pic 4 shows the sib unfolded and finally the transom.
I ran out of time to complete the job today but will try tomorrow.
I'm starting to think my idea of inflating /deflating after use is going to be wishful thinking... I feel a trailer purchase coming on.

MustRib · 06 March 2008, 22:50

YIKES !

150 kilos without a motor...its really heavy!
The transom looks twice as thick as the one on my Searider.
It should last forever though! Good luck!

bobbyjoeufb · 09 March 2008, 20:19

I used to use one of these when I was an instructor at the Sea Cadet Corps, we ran with a Mariner 40hp short shaft with prop guard.

Was great fun on flat water, but had a nasty habbit of bending and flexing in heavy conditions, make sure you keep your fingers away from the floor boards when under way or might lose them.

As for the bottom boards the flat one that is taped in the middle goes into the boat first at the stern. It should have blocks to guide the keel assembley into the transom. Then the heavy bottom boards and finally the wood pannel for the bow which is a complete pain to fit and takes a lot of kicking whilst pulling the front of the inflatable up.

As for deflating and reinflating I would suggest you get a trailer as the boat will last a lot longer being left inflated than rolled up.

Eugene Wixted · 18 November 2008, 15:57

I also bought one of these Geminis from JBT earlier this year.
I was considering a 2006 25hp Mercury 4 stroke to use with the SIB on standby/safety boat duty. The outboard is available from a dealer and seems to be reasonably priced.
Any comments good or bad on this unit.

Thanks

towersje · 18 November 2008, 23:40

Very good things to say about the Merc 25. We put them on our Commandos and they punt them along very nicely. Good fuel consumption, sensible shallow drive system (only one setting, but not a disadvantage where we were). Only problem we found was that the throttle would stick for a few seconds if run at flat chat - traced to a dodgy throttle rod. That was only on one unit though. I'm not normally a four stroke person but I liked it!

You can indeed carry them fairly easily - got to be a plus!

spartacus · 21 November 2008, 21:34

30hp 2-stroke would be your limit. I use to manhandle a 25hp Yamaha short-shaft by myself and it was challenging, especially on a steep or green slipway. Any more HP and you risk damaging your back and the engine itself!