Cat Design comparo question

Hi all,
First time posting in here. Currently researching my future boat build and narrowed down to Grainger Raku 48 and Schionning G-Force 1500C for family cruising. I love everything about speed and would love to occasionally be able to sail fast like high teens or even 20's. My dilemma is we all know performance potential of g-force line of cats, downside is building method too many curves and lots of planking involved (not sure about Arrows even if it's flat panel design). Grainger cats are gorgeous but after talking to both designers Jeff emphasis is on waterline beam ratio as well as light weight while Tony's claim if I want to go fast should look at power to weight ratio (keep the weight down) and cruising in high teens is a rare occurrence plus his cats offer bigger payload. I'm not planning to stuff the boat with all the junk and try to keep it as light as possible with only basic equipment like small Aircon for bridge deck, fridge and freezer and water maker. Now considering that both cats are built using the same method vacuum infused high density foam core with S2 glass and some carbon fiber reinforcements (both cats weight similar around 8 ton KG, use similar mast length) only difference is waterline to beam ratio 12.6:1(raku) vs 14.5:1(gforce) do you think that one will be superior to another as far as speed and comfort level going into those speeds? Just trying to chose carefully before committing to time spend to build plus $$$. Thanks in advance.
Geno

 

Hi Geno. What is the calculated wetted surface area for the two designs?

 

James,
dont know at the moment and it's not posted under both designs. Only thing I've found that is somewhat related to that is Hull Draft 578mm for Grainger and 550 mm for Schionning.

 

Personally I don't think you can go wrong with either option as they are both great boats. I think they both have some strip planking iirc but only in the hulls below the waterline and at the sheerline. It goes quickly there but I can see how it could be offputting for a home builder to some degree. Do you have any local boatbuilding schools that offer a strip planking course? It's nothing to be afraid of and is easier than you might think.

 

Corley,
Build method doesn't bother me as much as making right decision with the boat. In G-force there is much more planking or curved parts all over the hulls even on top, while Grainger is slightly shorter hulls are very tall and look humongous (headroom in the boat is over 2 meters everywhere) so it's give or take.
I'm in touch with one home builder who's in the process and it isn't that bad just a lot of work which I don't mind, he had build Grainger before and said that differences are minimal and come down to personal preference with g-force slightly faster at the penalty of a payload . Both have round bilges below water and that could be done using scorched foam with male jigs and battens.
In Grainger's design once you have bottom part of the hulls then its just a matter of flipping them and setting bulkheads and frames in the shoes and build from bottom to top mostly flat panels. Grainger encourages use of foam with matching density according to design which I prefer since I'm in US and use of wood or balsa is NO GO While Schionning prefers end grain balsa over everything, though foam is an option and he suggested new Divinycell over Corecell due to it's stiffness. I know g-force will be quick/er most likely just wish I could find any reference to Grainger Cruising Cats, Tony mentioned Chincogan 52 on which Raku is based on and claims it to be as fast as you want it to be. Bottom line I'll wait until one of Raku 48 will come out from Cure Composites shop and see what the verdict is. Thought that I'd ask you knowledgeable guys on this forum for your opinion and maybe even experience with both designs.

 

I checked both of them out too and like them both but Shionning doesn't provide CNC plans which made them a no-go for me. I don't know what was meant by sticking with the same density foam, you need high density in some areas to provide crush resistance, you can't get away from that. Also Corecell?? That is what I used to build my flats skiff but it's pricey. Next boat I build MIGHT use Corecell below the waterline, everywhere else it's going to be crosslinked pvc which is about half the cost and has been used for years with no problem. http://www.kelsall.com/TechnicalArticles/KCTheCoreOfTheSandwich.pdf

 

Geno You may see this build of G-Force 1500 in Holand in foam core.
Tri-Cat Sailing - zeilmee.nl https://www.facebook.com/Zeilmee.nl/

 

In practical terms squared off topsides are in my view more practical so the rounded sheers on the Schionning look nice but don't make the boat more practical. It does have some minor impact on ease of access forward. If you have trimaran floats for example which at times don't have much freeboard then rounding everything off can make sense but not much need on most catamarans.
'
Kelsall was a pioneer and is due some respect for that but ultimately most boatbuilding methods and materials will work assuming that proper care is taken of the boat. It's worth remembering that the shell amounts to some of the overall cost but a neglected boat whether it's made of steel, aluminium, ply, endgrain balsa or foam core is really the sum of the whole. If all of the equipment is worn out, paint isn't kept up and rig safety attended too it's not ultimately not going to be worth much or even be a good prospect to restore.

 

All valid points fellows!
Jorge - what I meant by matching density is matching according to design, I'm aware that density varies based on the placement and stress area. I'm willing to go even further as Jeff Schionning mentioned use of at least 100kg density PVC foam therefore less skins to be used to save the weight while being stiff enough (not sure if this is a good idea in the long run).

Bscatam - I'm in touch with the guy who's building gf 1500c using Farrier method which I'm not a fan of due to time being spend for female jigs and vertical strip layout.
Paul the builder is nice enough to answer any questions I've had and getting close to completion.

Corley - agree with you on topsides, but each design has it's own compromises like any boat in general Ideal boat would be GF 1600 SSS I was offered as a custom design (rounded bilge and flat panel all around + killer looks like GF 1800SSS) but the price admission is high and for the money I could get streamlined design and good chunk of materials for the project. Both models are so new that there are no reports of performance or good thorough review. Only one version of GF 1500c is on the water right now made by Northstar guys which if I go with I'd follow their method of building (they don't say much, only advert. the boat that is for sale for $1mil and claiming it can do 19knts upwind?). So I'm taking my time to get more info on both of them and getting place to build an launch the boat. For materials I agree but my mind is set on Foam core, balsa is no go for me it gets really cold in here during mid winter and wood has tendency to shrink then expand and ultimately rot and people here avoid them as plague.

 

Graingers design is a higher volume boat. It will be more spacious and be more suited to cruising and living on board.

Schionnings Gforce designs are significantly lower in volume. It will be more cramped and not as comfortable to live aboard. It should be faster/ lighter as it will have less surface area provided you don't overload it. This boat would be better suited to club racing with a little cruising in between = more bias towards performance as opposed to cruising.

 

Mmmm that G-Force 1500 racing version is calling my name lately, sailing that's what I'm after and even with that 1500 kg payload I think I could easily be even under that only thing I need is food water and some fuel for engines. Just a thought of sailing high teens comfortably makes me salivate, I'm a speed junky all my cars in the last 6 or so years were no less than 400HP and cruising in them at close to 100 MPH into fast turns (safely) was so easy and confidence inspiring that it became like a drug. Grainger on the other hand is stunning looking vessel and should be able to sail high teens if light, so I'll wait for reports from the owners and pictures once it's done. On the other hand Groper since you've built yours using Infusion method do you think that infusing the whole assembled hull vs infusing flat panels and taping them together with bottom shoe on the bulkheads? Which method is better and more solid, I'm thinking whole hull infusion will be more solid or there is no difference?

 

Theres no difference...

Whole hull infusion is great if you already have a mold- but since you dont its just way too expensive and time consuming to build a mold for a 1 off.

FwIW- the arrow series from schionning looks almost identical to the gforce but without all the compound curves. This is a much smarter way to go

 

Thanks man! Arrow is nice too but something is missing there, and that's where Grainger came up that has best of both - round bilge and flat panel up top plus all of the room and payload.
Do you suggest perforated vs plain foam for delaminations sake ?

 

There is no delamination sake. Foam and glass only delaminates if the design loads are exceeded - for example with high slamming pressures etc- or via poor laminating procedures used by the builder/laminator.

Perforated is for infusion or vac bagging processing and allows resin and or air to pass from the tool side to the bag side- no other reason to use it.

 

Thanks for the tip!