Category B boats

[Lordylordy]

Hello forum!
I have recently had to downsize from my Jeanneau Leader 705 - which is a category B boat, ie more seaworthy than category C boat - to a Jeanneau Cap Camarat 545, a category C.
I've noticed a huge difference in 'seaworthiness' in choppy water and wondered whether there was a simple way of finding out what boats fall into what category? It seems to be very rarely listed in ads, but is, to my surprise, quite a critical detail.
Cheers all,
Simon

 

[deepsix]

I suspect that the performance differences between the two boats in choppy water is more down to the size and weight difference than the RCD Category itself. There are plenty of seaworthy Category C boats. Hull design would be the thing to look at, along with length, width, weight, inboard/ outboard etc.

What specific differences did you notice?

 

[Portofino]

Another parameter to add to the above in my view the most important regarding sea " worthiness in CHOPPY " water is the deadrise .
Walk up to any salesperson in a blue blazer and grey slacks at Southhampton boat show and ask them "excuse me what is the deadrise of this " - and get a dumbfounded look back -I did !
It's a the ange of the V to the horizontal at the stern .Generally the deepess of the V of the hull -greater the better for ride confort .-in choppy water .

Thay all vary Why ? --- the Oppersite ie flatter aft sections give more lift .So it's a play off -lift ( smaller lighter cheaper engines ) Versus deeper V -better ride to part the wave as opposed to ride over and bounce /slam /cash land .
A deeper V has less lift so to plane it will need mores Hp ,more speed , bigger engines and probably cost more to make .
Also in bigger boats more aft volume inside with flatter aft sections ,ie for the current trendy "wife decision clincher ". Mid cabin .
How ever the principle of the deep V is the same in small boats re ride .
Another annoying modern boat show habit is coving up the below water line part of the hull with a skirt , so you cannot see the hull ,the steepness of the V .
Any thing over 20 will slice through , not slam .Some boats are a low as 12-14 -eek ! = real slammers
Every degree counts -mines 23
Take a walk around the boat yards ,or dry stack compare your V with the competition -there in is the answer to your Q

By way of example last week in a F6 I set off on a 2 hr 60 mile trip from an anchorage back to our marina ( forcast was even stronger winds ) Simultaneously a Managusta 108 on jet drives set off back too .-jets lift -flat aft sections
I got up 1st @ 28 knots cruise (backing down fron usual 30 due to 2 /3 M + ) waves ,he followed me and eventually sat in my wake for over an hour ,before turning off into S Trop .
Thing is my boat is 48 , -so ok size ,weight ,length kinda count ,but and its a big but --- hull profile ,deadrise trumps every thing .

 

[Whitelighter]

RCD does NOT test handling - it's all about stability. Most of the tests are done in a tank using weights etc

 

[deepsix]

Yes, by hull design I was touching on many things. Deadrise for sure, though there are, of course, some very seaworthy boats (that do not slam) that do not have deep v hulls with a high deadrise aft. For example, a Nelson 40. Fine entry, soft chine, flatter aft end etc. In this case I suspect that the size has made a big difference, especially if short wavelength chop.

 

[prv]

RCD does NOT test handling - it's all about stability. Most of the tests are done in a tank using weights etc

And some of them are simply design points, like location of doors and height of coamings.

Pete

 

[Nick_H]

Portofino, i'm no naval architect, but what's the point having a deep V in parts of the hull that never leave the water? I very much doubt a Mangusta 108 ever gets remotely close to being airborne, regardless of the sea conditions, in fact I doubt more than a third of the hull ever leaves the water. Do you think there could have been another reason he was following you, maybe he was just going in the same direction

I agree that aft deadrise certainly makes a difference with small fast boats though, like the ones the OP is talking about.

 

[deepsix]

I agree, on a small and fast planing boat then a high deadrise angle helps a lot. With larger boats I think a soft chine helps reduce slamming/ pounding, although generally more suitable for slower boats.

 

[BruceK]

I think the RCD CAT certs are misleading. Having a B or A does not make it more sea kindly from a comfort point of view to a C or the general perception of sea kindly at all. Chop has little to do with it. I went out fishing Sunday in a 16 foot cathedral hull dory that bloody nearly swamped on launching when it went beam on to a 30 cm shore break, yet when out at sea in very choppy water of 0.5m with a 3 second period turned out to be so stable you could stand two up and fish. In my boat we'd have been rolling about like drunks in that short chop and probably get a bit green. Yet this little affair was small enough that it just bobbed between swells quite comfortably. It was an eye opener for sure, yet nobody in their right minds is ever going to place a 16 foot dory at anything more than a D. God knows what mine is, it predates rating, but if rise is your criteria, she should fit the bill, I'd estimate 20 at least.

 

[MapisM]

Portofino, i'm no naval architect, but what's the point having a deep V in parts of the hull that never leave the water?

Well, the bow V angle is also somewhat related to the aft deadrise (which is more commonly used just because it's unequivocal, the V angle being possibly variable through the hull length).
That said, with all due respect for the legendary Itama hulls, I also doubt that the Mangusta 108 choose to follow Portofino for any reason other than because they just fancied to do so...

 

[PowerYachtBlog]

Hull study is not straight forward to dead rise alone. I know some flat Vee boats that in the right conditions cruise even better then some deeper Vee models length with length.

For example a Viking 52 or 55 Convertible has an 11 degree aft section but I am sure can give most boats a run of the money in rough seas.
Same as well with some of the Uniesse boats which close at just 8 or 10 degrees aft. The Uniesse 57 is incredible in head seas for example.

One of Bernard Olesinski best ever made hulls was the old Fairline 50 which has 15 degrees aft, this hull is even better then his normal (90s) 18 degrees stale mates for example.

Itama which have 22 degrees aft apart having an incredible dead rise have also a super balance, along with big study for an important 10-11 degree shaft angle.
I am a big fan of Itama and would certainly consider Itama as one of the ten best sea-keeping fast hull boats around.

And this all falls to one thing, that deep Vee hulls needs also a lot of thought in the balancing. So to be true for most cruising boats this is not so straight forward as one would think.

Certainly when you go bigger it is normal to have hulls closing aft at 15 degrees or less.

 

[Portofino]

Agree it's multi factorial --- ride
PYB says 23 here

Nick - just an observation re the Gusta 108 it anchored by us W of the Presidents Summer Chateau in the Var .Chater boat full of punters from st Trop -you know one of those premantantly moored .
Wind got up so off we both went .Set off back at 6 pm
I was surprised he did not come past ,or more over I could do that speed in those conditions .

We were not ,and either the Gusta getting airborne - i was just parting the sea ,cutting through it as opposed to bouncing over it .
Sure a 108 will not get air ,but 1/2 or 1/3 in the water ,if the front section that is too flat is bouncing then it may send horrible noises to guests -dunno .
Shaft angle - sure - Itama go to great lengths so much so they reposition the steering gear like this ( not mine )

Fine -entry MapisM -- yup

Thing is Op was asking /wondering what to look for -so I thought deadrise or the angle of V seen from the stern a pretty easy predictor of ride in a sea state , as any other hull indice is kinda hard to see /guage .?

From experiance that seems to be the case .

"hull profile " you can,t really ask the sales team to e-mail a CAD file of the underwater profile , kg wieght distribution , shaft angle etc and all the compuer simulations to my nominated Naval engineer / architect ,to cheeck and report back before buying a boat .

So what are you left with -boat shows where they hide the underwater sections from view

Suprised hull profile is so low down in the buying order , because it makes IMHO a huge diffenrce on how you can enjoy using the boat .

 

[Portofino]

Portofino, i'm no naval architect, but what's the point having a deep V in parts of the hull that never leave the water? I very much doubt a Mangusta 108 ever gets remotely close to being airborne, regardless of the sea conditions, in fact I doubt more than a third of the hull ever leaves the water. Do you think there could have been another reason he was following you, maybe he was just going in the same direction


I agree that aft deadrise certainly makes a difference with small fast boats though, like the ones the OP is talking about.

I used the Gusta example to kinda nullify the Op,s initial concept that boat length seemed to be it .
As 108 and 48 are miles apart .

Iam no naval architect either .Just observant . Watching Rivas and Itama slice through dead level while I bounced about in a Sunseeker.
One day a piqué of fit ( wife whingeing re ride ) we shot off in the car to Monaco Marine with a view of "I want one of those " after being overtaken by a Rivarama 44 on the way back in chop .
There it was plane to see the stern of one out on the quay , and talking to the guy - deadrise came up in conversation .
My guardiene put me off - maintenance issues and parts prices .

The point in having the deep ness of the V carried as much as one can to the stern isn,t about a soft landing -cos as you say we did not get airborne and the Gusta did not - it's more about parting ,cutting through , riding through not lifting up even at the stern .
Too much ( there's Allways some ) stern lift ,then gravity takes its toll and it may depending on wave period etc drop into a hole ,that otherwise would not have happened if it had not been so high / lifted up .
That's the point I think of trying to extend the V as far back -happy to stand corrected

The downer is you need more HP ie bigger engines and all that goes wirh that ,bigger tanks etc more £££ to drive it all .
Flatter aft sections can get away with smaller engines as they create more lift to get it planing cos it's got less Hp for a given wieght .some thing like that --I think

BTW -there's no noticeable hump - no popping up - just linear speed - I have no idea what planning speed is I can,t tell .

 

[PowerYachtBlog]

Yes 23 degrees deadrise for both 48 and 55.

The rest old 40, 50, and 50, and 76 have 22. 76 might be 21 but I do not remember out of my head.
Magnums have all 24 degrees, minus some of the early race boats which went as far as 26 degrees.
Baia have 20 to 24. 48 Flash for example is 22 degrees but rather flat entry of 32. The Azzurra (old B55, 59 Exuma) is definitly the best of the recent Baia hulls.
Otam have 24, they are very much a Magnum made in Italy for the exceptions of 80 (Buzzi Record), and 65 and 50.

I think with hull design it is important to know the limits of your boat. My Gobbi has 15 degrees deadrise aft, is she a bad boat in bad sea condition no.
Is she the level of an Itama surely not. But thanks to extended plane she can cruise at 16/7 knots in Force 5 winds 2 to 3 meters waves in rather okay comfort.
Some deep Vee actually hulls cannot do so good, cause at that speed cannot go on plane very well.

Mangusta where never special for rough seas to be honest, Arno Leopards where always better, but the new models have improved a lot 110 and new 94 for example are much better then 108 and 92.
They learned a lot from the building of the 165.
I would have always suggested as something similar an Italcraft, Alfamarine, or the Leopard. Possibly in that order with the first two being very close.

I am sure the Poster of this thread will want to kill me and you Portofino for the off topic.

 

[Portofino]

Arno leopard is my lottery win boat .
Hull looks right above and below water ( saw both Gusta and leopard out @ San Remo once )
And the bow flare is just superb

Flat sea here
Btw I came behind him @ 28 knots -he went up to when a got along side to 32 , I went up to 36 with some spare .,- just incase - but did not need it
We both eased off when I was 1 mile up the road- don,t ask how many L/hr was showing -well it was only 10 mins

Sorry for the thread drift Op