cat-hulled SIB questions

[BC'er]

Greetings all,
I have been scouring this forum for information regarding inflatables, and discovered the Gemini 420 and 470, which look like a good fit for my application/s. I am looking for a safe, seaworthy boat capable of of being beached, for day and overnight trips on the west coast of Vancouver Island near my home. I want a safe boat for short trips with a family of four, as well as something that performs well in waves and swell for more adventurous trips with friends to remote surf locations.
I do have a few questions however, mostly concerning trailering and launching. I hope those of you with experience with these boats can help me out. I have a background in river rafting and kayak guiding. I find it interesting that hypalon seems to be preferred over PVC for SIB construction, in fact I believe Gemini themselves provide a longer warranty on their hypalon boats. Most people in the rafting business abandoned hypalon for PVC long ago. I have run both hypalon and PVC rafts in whitewater up to class IV, and found the increased rigidity of PVC made it much less susceptible to holing/tearing. On multi-day trips in the Yukon/Alaska we used fully loaded 18' Maravia rafts (PVC), which took an amazing amount of punishment. I thought the only advantage to hypalon was it is much easier to patch in the field. That said, in my days as a river guide, I patched a lot of hypalon, but never once a PVC boat. But I digress. On to my questions:

On a trailer, does the engine have to be supported independently to avoid strain on the transom? If so, how is this done?

How exactly do the launching wheels work? Can these be purchased or is this something I would have to have custom made?

Is it possible to install seats in these boats for my kids so that they don't have to sit on the tubes?

In order to get the boat up and down the beach to avoid the tides, I would obviously want to use as light a motor as possible. Considering a 30hp e-tec (146lbs). Would this be enough to power these boats adequately?

This is a great forum. Thanks in advance for any help or or suggestions you can provide.

[prairie tuber]

Hi BCer,

Welcome to a fantastic site!

Whereabouts are you? Port Refrew? Tofino/Uculet? Gold River?

I'd recommend getting in touch with Rob or Trish from Hi-Tech Inflatables in Parkesville,

( http://www.racing-inflatables.com/surf.htm )

or Anthony at Orca inflatables in Vancouver

( http://www.aluminium-ribs.com/en/products/gemini.php )

or, take a trip over to sunny, warm Manitoba (the ice should be off the rivers and lakes in the next few weeks), and I'd be happy to take you out in my hypalon Dive 470.

Rob at Hi-Tech has a demo model PVC Dive 470 with double skinning for extra abrasion resistance. He might also have a surf 420 on hand as well.

The PVC boats tend to be a bit more rigid because of the material is less elastic and that they can be pumped to a higher pressure. For a boat designed to be as high performance/and light as possible such as a zapcat, PVC would have clear performance advantage over the same boat in hypalon. For a heavier, more utilitarian boat such as the Dive 470, the performance differences between PVC and Hypalon would be much less noticeable - especially if the PVC is double skinned.

Hypalon will have far greater resistance to UV degradation than PVC (although both materials should have a tarp cover when not in use). Hypalon will also remain more supple and will not fatigue harden over time like PVC will. Hypalon will also maintain that suppleness in the cold and is also less affected in very hot conditions. For me, this is very important because in Manitoba the temperatures have an 80 C range from winter lows to summer highs. I've used the boat in Mid-late November here, where on the faster flowing rivers, the water might still be open at -20C. A PVC boat would almost certainly crack at those temps. This is probably a non-issue on Vancouver Island or the mainland coast.

Gemini hand glues the seams of these boats regardless of whether it is hypalon of PVC, which is a good thing because it makes them repairable.

I have not had personal experience with the surf GRX 420, but from what I understand they have almost zapcat-like performance with the practicality of a round nose. 'Ed the Duck' on the board here has one in hypalon, and I believe there are a couple of guys on here with PVC versions as well. 'Easy Rider' has a Ceasar Surfcat which is very similar to a PVC Surf GRX 42O. Not to put words in their mouths, hopefully they'll chime in, but I know that they are extremely impressed with the performance and quality of these boats.

I struggled a bit deciding between the GRX 420 and the Dive 470, but decided on the extra space and weight capacity (bigger tubes) and general bombproofness of the 470, at the expense of the extra performance of the lighter GRX 420. I also went with floorboards that were thicker (3/4") than standard (5/8") for additional rigidity with heavy loads.

As for power requirements, I have an older 2 stroke Yamaha 40 which will give me close to 40 km/h with me and another couple hundred pounds of gear & fuel in the boat. I would expect that one of those new 30 hp Etecs would perform pretty close to my older 40. If you were to put that on a GRX 420 (which would weigh about 150 lbs lesse than my boat) I'm sure that you'd be able to go considerably faster your average passenger would like.

As for seating, there are all sorts of things that can be done with some fabrication. I much prefer that my passengers sit on the sponsons while I'm piloting the boat so I can see where I'm going (I sit forward facing on a seat while tillering with my left hand). With the 22" diameter sponsons, the sitting height for the passengers is very comfortable, and they are well 'inside' the boat.

[reinier]

A 30hp E-tec won't perform like a Yam 40hp 2-stroke, maybe not even like a Yam 30hp 2-stroke.

I think 30hp is a little underpowered, would suggest a 50 at least, because the engine will have to work less hard for the same speed (= less fuel if your @ a nice cruising speed).

[prairie tuber]

I think our perspective on what is 'sufficient' horsepower is markedly different.


reinier
Member


Country: Netherlands
Town: Holland
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Make: Brig F360S
Length: 3m +
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Join Date: Jan 2008
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[Ed the Duck]

BC'er,

I opted for a Gemini Surf 420 in hypalon 5years ago, primarily because I wanted a bombproof boat, suitable for use in surf and for 10-20NM passages, that I could drag up and down beaches and not worry too much about wear and tear.

I'm not sure what the Gemini waranty is for hypalon, but my boat has been used heavily for expeditions and playing in surf and is showing no real signs of wear.

I guess that PVC may be more suited for rafting because of the frequent contact with rocks. My experience with RIBs and SIBs is that the wear tends to come from passengers, cargo and fuel spills. It tends to be the glueing rather than the fabric that fails - fortunately the build quality on the Gemini is sufficient that none of the original construction has failed.

As for a family boat, I have a 40hp 2 stroke Mariner and I would suggest that you do not need anything bigger. 40hp is more than sufficient for operating in powerful surf and gives me a loaded top speed of around 25kts. A 30hp 2-stoke may prove to be more practical for launch and recovery. (Toby Budd used to post on here and his pics of the Surf 420 operating with a 30hp 2 stoke are pretty impressive.

Like all small SIBs, the 420 has relatively small tubes if you wish to sit on the sponsons. I have had to fit toe straps to the floor. In bigger seas I sit on the (padded) floor and brace my legs against the opposite sponson. Seats could be possible, but the bouncing around of your passengers may make them too uncomfortable or dangerous. I would suggest that the 470 may be better for a family to ride in.

[jyasaki]

To answer your other questions (I have no experience with any of the models you talk about):

Originally Posted by BC'er

Greetings all,
On a trailer, does the engine have to be supported independently to avoid strain on the transom? If so, how is this done?

Can of worms, as everyone has their own theories and beliefs. It should be done (IMHO); especially if you are trailering on less than baby-butt-smooth roads, with larger engines (i.e. more pendulum mass) needing it more. Bouncing at the wheels transfers to the motor, and causes the motor to pendulum through it's (admittedly small) range of play, creating a yoyo effect that is absorbed by the transom and transom supporting areas.

There are a few ways of addressing this, here are a couple:

Many people simply stick a block of wood between the motor and the mount, and lower the motor onto it. This reduces the amount of play (essentially overrides any freeplay in the tilt/trim.) It does not (again, IMO) reduce stress on the transom (or if it does, not much.)

A second option is to use a "Transom Saver" or motor support bracket; this is a rod that mounts to a trailer cross-member, and the lower unit sits in a cradle at the other end. This transfers some of the energy from bouncing to the trailer frame, lessening forces on the transom. By supporting the LU, you eliminate the penduluming of the motor, and keep the fore/aft movement of the transom to a minmum.

How exactly do the launching wheels work? Can these be purchased or is this something I would have to have custom made?

They are wheels at the stern that are (usually) lowerable to move the boat, and raisable for traveling on water. You lower the wheels, and move the boat much like a wheelbarrow, down to and into the water. Raise the wheels, and motor off.

Not much use on a heavy boat. I know that my 14' Achilles/Honda 40 would have been impossible to launch that way without about 4 guys. 6 guys probably could have picked it up and tossed it (not literally) in the water.

They are sold commercially, though whether or not you can find something that will work for your application is a bit of a crapshoot.

Is it possible to install seats in these boats for my kids so that they don't have to sit on the tubes?

Yes. They may find it more comfortable on the tubes, though, depending on age. Tubes have a natural shock absorption built-in.

Luck;

jky