hull extension

[Nick_H]

The Princess seems to run better with full tabs down, even at the fastest cruising speeds, and I much prefer a more level running trim. I'm about to add another 500 kgs to the aft end with the gyro, so i'm considering a hull extension a bit like this:

Our old Sealine T46 had such an extension, as do many other boats, presumably added on after intial hull trials to fine tune the trim. The effect would be small of course, but I could fabricate it to run a few degrees out from the line of the keel to provide a bit of extra lift at the stern. The cost of fabricating and fitting it is pretty negligible so I could just try it, but it probably means bolting through the hull unless I could epoxy it, but then it's difficult to remove if I don't like it.

Have I missed any unwanted side effect on handling or efficiency?

 

[[2068]]

I'm not sure about having it angled downwards - that would be like having a centre trim tab permanently applied, which might destabilise things at vMax.

Have you considered fitting larger trim tabs?

 

[jfm]

Hi Nick
Engineeringwise it looks sensible to me. Through bolted I think, and a bit of downward angle would be fine imho

You have to be careful in this desire to have the boaty trimmed flat. The boat only planes if there is a bit of nose up (Newton) and Olesinki hulls generally need a bit more becuase the keel at the bow is deeper than at the transom hence they have a bit of natural negative angle of attack at rest

But the new 500kg you are adding would likely need some compensation so your idea looks good. On the Sq78s (2 off) that had twin gyros they ballasted the bow to correct the effect on trim

I chatted to the american guy on the Seakeeper stand at Canes show yesterday. He said he knows you - has been dealing on your purchase. Nice guy and knew his gyro physics. The unit you are buying (with updated software/algorithms for the precession control) sounds very good. My one worry, because of the fact you're putting it in lazz not e/room, is noise. It would be a shame to have a nice unrolly boat with a whinning noise. It would be worthwhile paying attention to managing the noise the noise by putting some lagging or whatever in there, or one of Ellessar's lead blankets over the whole installation

[Completely o/t point: I looked at the boat to your port side and it's easily 5.6m]

 

[Nick_H]

Have you considered fitting larger trim tabs?

Yes, but that means more load and may involve bigger actuators, and maybe even a bigger pump, although I haven't looked into the detail of my system, and it may have some capacity left in it. I just thought that if I always want some more tab, then no harm in having it fixed rather than adjustable, and it seems easier to bolt something on.

 

[Nick_H]

You have to be careful in this desire to have the boaty trimmed flat. The boat only planes if there is a bit of nose up (Newton) and Olesinki hulls generally need a bit more becuase the keel at the bow is deeper than at the transom hence they have a bit of natural negative angle of attack at rest

Point taken, although the hull on the Princess already extends half way under the bathing platform, so i'm talking about a relatively small bracket which isn't going to have that much impact on trim

I didn't realise Andrew from Seakeeper was going to be at Cannes, or i'd have made the effort to go, as i've only communicated by e-mail so far. Yes, I plan to go overboard (scuse the pun) on noise reduction, not just the gyro but the genny as well so it's not too intrusive in the cockpit.

Interesting point on the beam of my neighbours boat. You probably know that he was previously on a 23m berth further down the quay, very close to your new berth IIRC. I'm writing to the port about it, hopefully they'll be able to move him where there's enough space (I also wont miss him sitting in his undies watching porn with the curtains open)

 

[jfm]

Point taken, although the hull on the Princess already extends half way under the bathing platform, so i'm talking about a relatively small bracket which isn't going to have that much impact on trim

I didn't realise Andrew from Seakeeper was going to be at Cannes, or i'd have made the effort to go, as i've only communicated by e-mail so far. Yes, I plan to go overboard (scuse the pun) on noise reduction, not just the gyro but the genny as well so it's not too intrusive in the cockpit.

Interesting point on the beam of my neighbours boat. You probably know that he was previously on a 23m berth further down the quay, very close to your new berth IIRC. I'm writing to the port about it, hopefully they'll be able to move him where there's enough space (I also wont miss him sitting in his undies watching porn with the curtains open)

Yup, that was his name, Andrew. I said a friend was having the ex demo unit and he immediatly said "You mean Nick?" so he is the guy you're dealing with. Nice guy and v knowledgeable on the physics of gyros. He showed me the product in detail (they have 2 units there on the stand) and we had a nice chat. He might have convinced me that on an ideal boat you'd have gyros AND fins . Show is on this weekend if you can get there - I have a small stash of tickets. Good plan of yours to deal with the noise

Good about the badly behaved neighbour. He is easily a foot over, each side. Your fenders are squeezed hard. I thought there was a no black waste rule in the port, and there might be a no liveaboard rule but I'm not sure, so there are several bits of the book to be thrown at him

 

[Deleted User YDKXO]

Glad to see that its not just Ferrettis than run faster with a fair bit of tab down. I would be very cautious about adding fixed planing tabs at the transom for a number of reasons. First as jfm has pointed out, there will be times (ie a big following sea) when you really dont want any tab down. Second you don't know how it will affect prop and rudder performance. I was once told by a Sunseeker guy that the fixed tabs on the back of one of his boats was necessary to improve rudder performance, not planing performance.
IMHO, whilst 500kg is a fair bit of weight, its not that much. its equivalent to having another 500litres of fuel in your tanks or having 4 fat blokes sitting in your cockpit I'm sure a P57 can handle that

 

[PowerYachtBlog]

I honestly want do the hull extension until I try how the boat handles with the Seakeeper gyro and its weight.
If I see the boat suffering after that then I would contact Princess.

My friend had a similar problem with a 44 Manhattan and he was gonna go a similar route to the hull extension pictured, simply because all the 44 Camargue's have it.
He on the 44 Manhattan a Zodiac 350 Jet Rib on the b/platform which has lost some speed and made the boat ride quite bow high.
He contact SS and very helpful they tell him not to do it, but add like steps to the tabs which has improved results, much more then imagined.
They told him the hull extension would make rudder a bit fidgy and create extra useless drag, and there was no 44 Man fitted with it.

 

[Deleted User YDKXO]

He contact SS and very helpful they tell him not to do it, but add like steps to the tabs which has improved results, much more then imagined.
They told him the hull extension would make rudder a bit fidgy and create extra useless drag, and there was no 44 Man fitted with it.

Thats odd because the SS I looked at which had the fixed tab extensions was a Man48 and the salesman told me they were fitted to improve rudder performance

 

[MapisM]

I would be very cautious about adding fixed planing tabs at the transom

+1.

Otoh, 500kg "at the aft end" indeed IS a lot, also on a 57 footer.
Whilst I supported the idea of gyros in the previous thread where Nick anticipated his project, I didn't understand that the placement would have been that far from the CoG.
Not a good idea, imho.

 

[Deleted User YDKXO]

+1.

Otoh, 500kg "at the aft end" indeed IS a lot, also on a 57 footer.
.

I don't agree. My 53ft boat carries 2500l of fuel which is 2500kg as near as dammit. So the weight of the boat can vary by nearly 2500kg between full and empty and whilst there is a difference in performance between full and empty, its not huge. Yes I understand that adding 500kg near the stern is not going to help performance or trim but NickH could counter that to some extent by not filling his fuel tanks to max unless absolutely needed

 

[jfm]

Just to see the position of the weights, the wing fuel tanks (~2500kg) are clear in the picture below and the 500kg gyro is going in the lazzerette which is directly under the aft floor hatch in the aft cockpit (ie the bigger of the two floor hatches aft of the glass patio doors). The transom is (underwater I mean) about 1/2 way fore-aft under the swim platform

 

[Deleted User YDKXO]

Just to see the position of the weights, the wing fuel tanks (~2500kg) are clear in the picture below and the 500kg gyro is going in the lazzerette which is directly under the aft floor hatch in the aft cockpit (ie the bigger of the two floor hatches aft of the glass patio doors). The transom is (underwater I mean) about 1/2 way fore-aft under the swim platform

Yup, I understood that the gyro is located further aft than the fuel tanks but I still don't think that 500kg in the lazarette is going to make a big difference to trim or performance on a 57 footer. After all, for sure the P57 will have been designed to be fitted with additional equipment that NickH probably doesn't have on his boat like twin gennies, twin a/c plants, watermaker etc, all of which could add considerable weight aft. Another thing he could do is add weight forward. A big feck off anchor and an extra 100m of chain would help keep the bow down

 

[Nick_H]

He contact SS and very helpful they tell him not to do it, but add like steps to the tabs which has improved results, much more then imagined.

I quite like that idea, same principle as the VP trim tabs that extend vertically downwards. I could just bolt some SS angle, or even lumps of plastic, to the underside of the trailing edge of the existing tabs, and they should have more effect. Also easier to take off if the effect isn't what I want. I'd need to check on the ratings for the tabs though, as it would increase the load.

 

[Nick_H]

I still don't think that 500kg in the lazarette is going to make a big difference to trim or performance on a 57 footer

Agreed, but I always run with full tabs down now, so even a small effect on the trim will be unwelcome. It's mostly about personal preference, I like running with a more level trim, and I find no adverse impact on speed or handling, if anything I find it better.

 

[Deleted User YDKXO]

. I'd need to check on the ratings for the tabs though, as it would increase the load.

Definitely on that one. You could easily blow something in the hydraulic system by overloading the tabs. How easy or difficult would it be to simply upgrade the tab system to a larger unit?

 

[MapisM]

Yup, I understood that the gyro is located further aft than the fuel tanks but I still don't think that 500kg in the lazarette is going to make a big difference to trim or performance on a 57 footer. After all, for sure the P57 will have been designed to be fitted with additional equipment that NickH probably doesn't have on his boat like twin gennies, twin a/c plants, watermaker etc, all of which could add considerable weight aft. Another thing he could do is add weight forward. A big feck off anchor and an extra 100m of chain would help keep the bow down

Mike, I must disagree on all that.
Nick is telling us that his boat runs better with "full tabs down, even at the fastest cruising speeds".
This means that, no matter how many equipment she's designed to hold, in Nick's configuration she's already too heavy astern.
A permanent 500kg addition astern can only make things worse - though based on the drawing jfm posted, the position is not as bad as I initially understood. Still bad, anyway.

See, simply put, the two key factors in the design of a proper planing hull are
1) shape (obviously), and
2) weight distribution.
But the second is as important as the first: it's the combination of the two which makes (or not) a proper planing boat.
Btw, you always must aim at LIFTING, never at weighing down.
I recently gave my view on that in this other thread. Ballast on a P boat is something to avoid like the plague.

 

[MapisM]

upgrade the tab system to a larger unit?

THIS could be an idea. Possibly longer, rather than wider.

 

[Deleted User YDKXO]

Nick is telling us that his boat runs better with "full tabs down, even at the fastest cruising speeds".
This means that, no matter how many equipment she's designed to hold, in Nick's configuration she's already too heavy astern.
.

No it doesn't mean that at all. It means that the designer has given some thought as to what effect the tabs will have. If the optimum speed is achieved with tabs down, then the helmsman always has an option to bring the tabs up to bring the bow up for safer operation in, say, a big following sea. If the optimum speed is achieved with zero tab, then there is no option to bring the bow up further and worse, using the tabs could bring the bow down into an unsafe attitude. The most dangerous situation for a planing boat is not having enough bow up attitude and stuffing the bow into a wave. In any case I suspect that NickH's boat behaves like mine (flame me if I'm wrong!) in that the faster you go, the less tab you need to achieve optimum speed. At max rpm, my boat needs just a little tab to achieve optimum speed but at lower rpm, it needs more tab to achieve optimum speed and at minimum planing speed, it needs max tab to achieve optimum speed

 

[Nick_H]

How easy or difficult would it be to simply upgrade the tab system to a larger unit?

Well, not difficult of course, but 2 x new pumps, 4 x new actuators, 2 x new tabs plus ancilliaries and fitting (at SoF prices) is still going to be '000's I would guess, and more hassle to organise, for something I don't need (ie. more variability than existing tabs can provide). Fixed tab is free to me as I employ fabricators, and i'd just fit it myself next time boat is out the water. Simples.