gemini workboat antislamming

This is the underside of a GRP workboat from Gemini Workboats ltd. meant to prevent slamming in heavy weather from what I gather. Would it be better to have a different hull form prevent the need for such "outgrowths"?

Luc

 

Is there no slamming over the outer side of hulls?

 

I guess ther ain't no bridgedeck ?

pogo

 

is the boat running in planing or fast displacement mode ?
Having single chined hulls it should be planing mode, narrower and longer sprayrails , at the tailing edge about 20cm above CWL and angled 3Degrees might help. Sprayrails not only deflekt the water, they also generate better trimming angle.
Here, somewhere in between, you'll find a pic of sprayrails, but, yours should lateral be negative angled , alt least 90 Degrees (similar as outer stringers on planing motorboats)
http://forum.yacht.de/showthread.php?98827-Farr-goes-retro&highlight=farr goes retro


Running slow in displacement mode-----I have no idea.

pogo

 

This hull appears to be a cat, not a tunnel, so water is being displaced into the tunnel underway. Tunnel height seems not to be that great. Are you sure these appendages are designed to reduce tunnel slamming ? Are they something the boats always carried, or appeared later ?

 

Planing, good trimming angle.
Notice spray between hulls ! Generated either by poorly designed deflectors ( see above) or much too low bridgedeck, perhaps both.

http://www.bluewaterboats-plymouth.co.uk/southboats-catamarans-photo-gallery.htm

Sprayrails on the inner side of the hulls should be designed similiar as ( to ?) those on the outer side ( as described above).
Outer stringers on the Kimm --the edge of the hulls - should help also.

Sprayrails and outer chinestringers
http://www.fishyfish.com/img/sprayrail_hull3.jpg

pogo

 

If the boat is skating along on its tunnel, because it is low, and/or the boat heavy, nothing much will help the slamming. I am a little intrigued by those appendages, which have the characteristics of foils to some extent, looks more like an attempt to generate more lift at speed when the bows drop in, such as running down-sea, even a way to get more lift for the lower, "lee" side when stern quartering. I'd be interested to hear what forumite Alik thought about them.

 

found the following in marine-world.com

 

Wat für'n Schiet !!
vor de patat en bierkonings: Quelle merde !!
4 yanks and John Bull: What a ******** !!
( 8 stars can be translated-- Bockmist)

pogo

 

better overall view

can be found on gemini fastcat for sale

 

and in action

http://www.youtube.com/watch?v=m1HjOGGK6tc

 

There are ostensibly only 2 ways to prevent slamming:

1) Increase the wet deck clearance beyond the sea states the vessel shall encounter
and/or
2) Reduce you speed when the sea state increases....i.e. exercising good seamanship.

 

Well, instead of my just wondering what Alik might think, we now have an opinion from cat expert Ad Hoc. Have to say the clearance does not look to be that good.

 

The image above suggests a bandaid was applied after the first few hulls popped out of the mold and where tested. At certain speeds, I can see these deflecting portions of the inner bow waves, possibly to correct wet deck slapping, though also possibly to address other issues. The fact these are mechanically fastened is telling and maybe they need to reevaluate their multihull design team, more so then apply crutches to the inside of the hulls.

 

Yepp, you got it.

Here again the manufacturer's statement :
" Gemini are still the only cat builders in the UK that address the slamming problem and we have eliminated it on all our vessels."
Quelle merde !

pogo