Achilles su-14 mod

[oztrax]

Hi all,
new member here
got an Achilles 2.3 and a SU-14

they are well made but both need a bit of fixing atm.
the smaller one may be not repairable as one tube is torn.

The SU-14 been in storage a couple of years but was going well last time we took it out.

We had a Yamaha 30 hp 2 stroke outboard, could get about 15 knots with 3 adults onboard.
2 of us could just lift the outboard on, so wouldnt want to go much heavier.

[oztrax]

Our favourite camping spot is a dam which is fed from a pristine rainforest river,
part of a hydroelectric scheme.

I take the Honda F12X jetski as we have to traverse the whole dam and some of the river to reach whitewater rapids which are pristine and full of fish.

Jetski is doing close to 40 kts to get to this area in 10 -15 mins.
A dinghy with a 15hp took 1.5 hours.
So i need to either tow the 14 foot achilles or design/build a hybrid of the two.

[oztrax]

So, first step was to design and build a folding storage system for my jetski trailer to be able to take the SU-14 on top of the jetski.

I made this out of 4mm aluminium, steel was out of the question for weight, as this would of exceeded the GVM of trailer, which is 750 KGS

The rack/system, folds down after the jetski is removed to allow the inflatable to then be off loaded into the water much like a conventional trailer would.
A small winch is required to retrieve the inflatable, raise the storage rack and then load the jetski. Book weight for SU-14 is 110 kgs, but i intend to replace the existing floor with something else.

[oztrax]

I am waiting on 2 air valves fro the SU-14 before i can do a few trials raising and lowering the rack. I am confident this will work OK and am writing this thread as a help for anyone else who needs to carry 2 boats on one trailer.

But what i want to build now is a jetski extender out of the SU-14.
These are all the rage , the one below has a soft bottom and is a few inches horter than the SU-14.

[oztrax]

Higher end jetski boats/extenders usually use a custom built RIB design.
not cheap some sell for over $20000 USD.

The advantage is the jetskis power to weight ratio, mine is 170 HP and weighs 350 KGS all up. It will do over 100 KPH easily. and you can sit at over 40 knots all day. Combine this with the space of an inflatable extension and you have a RIB/SIB that will cruise at 40 knots and still be able to fold up at the end of the day or easily trailered.

[oztrax]

Attached design sketches are to scale as best i could, at that stage i intended to use the existing alum floor panels, but now i will make a single floor panel out of foam and fiberglass.

The SU-14 is a bit longer than the the jetski (11 feet) and the storage rack i built. this shoud not be an issue as the rear air cells will be deflated after loading onto trailer rack and then the last 1m of transom is folded over the rest of the boat.

The last 2 pics are from an existing SIB extender which is about 13 feet.
note the jetski is wider by 400 mm , the idea is to cut the existing transom plate in half and reshape to hold the jetski hull. Details in next post

[oztrax]

Attached some photos of how the jetski fits in, this one is a cheaper version of the SIB from the last post. WRT to my 3 designs from previous post, i will most likely go for the one with 1.5 floor panels removed, eg EXT3.

The pics can be quite decieving to look at, as jetskis are a minimum of 10 feet long, to position the jetpump thrust around the transom area, you lose a lot of deck space, in fact half of it.
Most of the better extenders are 5 or 6 M RIBs and require over 150 HP

So what im asking is for some expert hydrodynamic opinions from you folk before i start cutting up the Achilles.
I read where someone wrote here about tryin to dirve a SIB without floor panels and it just folds in 2, so my custom floor panel is a neccessity. The existing transom on the SU-14 is very heavy, i reckon i will save quite a bit of weight without it.

Also hoping someone on the forum might get inspired enough to do the same.
a jetski can plane in about 2-3 inches of water, i do it regularly (tight sphincter required), you can also go over small sand banks etc,
so a SIB/RIB under jetski power could be a very capable boat.

will put up some of the bigger RIB designs in my next post.

OZ

[oztrax]

Attached some of the larger RIB based jetski boats.

I have been studying these to see exactly where the jetski thrust is positioned.
It appears the inlet for the jetski jet pump,
(which is usually part of the flat metal ride plate and is designed to allow the jetski to plane with minimal hull in the water)
is positioned where the transom would of been, eg like if an outboard was installed.

So my rough plan is to cut the SU-14 transom in half vertically, then with the jetski hanging in my garage, back the inflatable in on my spare trailer.
then guesstimate and trim the transom to allow some sort of reasonable fit for the ski hull.
Part 2 build a one piece lightweight floor to fit in the forward section

[pumpkinking]

This does look awesome... more strength to your arm! Watching with interest.

[oztrax]

Looks like my RIB is an Achilles SU-16 not a SU-14..........

Which works out better as the width to fit jetski is perfect, within 30 mm

I have to keep the weight down to carry inflatable on top of my jetski trailer.
Book weight for SU-16 is 160 kgs !

Have removed transom, it weighed in at 22 kgs.
Large ally floor boards were 18 kgs each.

The front 2 fiberglass floor sections together were 18 kgs.

So with just the smaller front boards installed should be around 84 kgs.

Still have to make up a floor section out of foam and flowcoat.
hoping it will b no more than 15 kgs.

Has anyone else made up their own foam/fiberglass floor boards ?

Also attached my hull serial number, is there anyway to determine year of manufacture from this ?.

Last pic how i hope my build to look

regards
OZ

[oztrax]

Ok
so jetski is 200mm wider than SU-16, so made a temporary transom out of 15mm ply, released the floor rubber a bit around the original transom attach and squeezed it in.
You can see the white outline of the narrower original transom on this pic

Now to measure the inside width and adjust rubber floor if needed to squeeze ski in.Then i can make up new floorboard out of medium density foam and fiberglass.
The "legs" at aft end will actually be the original alum floor locking beams and will pivot in and out for finer adjustment and securing of ski to boat.
Also i am overwidth when boat is on top of trailer rack so will be able to let rear tubes down and/or pivot aft tube ends inwards.

Question I have would it be fair to say thrust on theses inflatables is mainly transferred thru the floor structure or the tubes ?


OZ