The Shipyard ( Dry Dock ): Builds & Questions > Sports Boats R&D:

Offshore Racing Boat - Best to build light weight or heavy?

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craig dickson:
Hi Folks


My topic question might appear somewhat simple compared to the more technical topics that we enjoy. However I am interested to hear your opinions as to whether you recommend building a boat that is as light weight as possible or perhaps more on the heavy side.


Assuming that the chosen IC power plant has sufficient grunt to get the boat well on its chines and planing as it should, what is your preference in respect of the overall weight of your boat?


Is it best to build with minimal weight?
Or better to make it heavier?
Or does it not matter a jot so long as the boat it properly trimmed and adjusted?


If you have a preference, please enlighten us with your opinion(s).... :-)


Cheers
Craig

w3bby:
Are you talking layup of the hull or overall weight?

As light as possible without losing strength... Building a light boat enables you to use weight, should it be required, to trim your boat optimally for the running conditions.

On M-course racing or other courses with sharp turns you will benefit from better acceleration with a light boat. However, if you are going to be banging about on the sea then a heavier layup is probably a good idea.

spearfish99:
Hi Craig,
 I would err on the side of a bit more weight. Possibly because that's the way mine usually come out!   Seriously, I think that balance is more important than the overall weight per se.  I know that lots of people quote the 30% from the transom C of G almost as gospel, but my observations over the years, it depends very much on the hull form. I know that we are probably talking deep v , but the angles of the v can vary quite a lot.

 From memory, my old Swordsman had a reasonably forward balance but ran nice and flat especially in rougher water. I am hoping that my A class Crusader 3 when it gets finished runs similarly.
 
Also think that one needs to consider the drive format i.e. do you use a stinger type drive , angled underwater drive or what ? Personally, where I can, I use what I would call conventional fixed sub surface drive angled down from the bottom of the hull. I don't say this is best, but it is what I get on with best given the type of hulls i want to run.

craig dickson:
Hi and thank you for your interesting input :-))


To answer the questions asked:
I am talking about the overall all up racing weight of the boat, assuming C of G in the correct place.
I am interested primarily in the boats that race around oval courses as opposed to an "M" course requiring tight turns. Including those with surface drive and submerged drive.
Although all contributions and considerations are of interest to me here. :-))


I totally accept as I am sure all will agree, that the light weight boat has a big advantage in terms of better acceleration, compared like for like.


However on a big oval course (such as the ones we have in BMPRS events), does that advantage come at a cost?
The reason why I question this, is that throughout the many exciting 2014 races, although we had great dry weather in the main, there were plenty of  occasions when the wind was extremely blustery! And there were memorable occasions of wind getting under the hulls of boats of all sizes and shapes leading to some spectacular flips and somersaults!


So as I see it, my train of thought is that a boat with extra weight as low as possible in the hull could be beneficial as follows.
1) Less top heavy means less chance of flipping over.
2) The natural extra inertia may help reduce the impact of a sudden gust of wind.
3) Similarly in the event of a small collision with say a buoy or another boat, less chance of the boat being violently knocked off course and a potential stop.
4) If the extra weight comprises of reinforcement materials in the base of the hull, extra strength and stiffness is an added bonus.


Now of course I am not suggesting that boats should resemble tanks, because tanks are known as being slow! Some might say that heavy boats will naturally be slower, but my thoughts are that so long as the power plant gets the hull riding sufficiently on plane so that the wetted area is identical to a lighter weight counter part, the straight line top speed should be just as good. Debatable perhaps?


In terms of acceleration, the other consideration other than going from zero to 60mph, is change of velocity in respect of turning ability. The lighter boat may require less force to turn it especially in a sharp turn. I say "may require less force" because if comparing two identical boats, the turning force needed for the heavier of two identical boats will depend upon where the extra weight is distributed. If the extra weight is all at the bow and transom,  inertia will require more force to turn it. If the extra weight is all around the mid section of the hull perhaps the boat might be more likely to spin when not wanted in a sharp turn?


Tell me please if you disagree as I am only thinking aloud here. My feeling is that weight could be used to big advantage in terms of making a boat more capable of winning races.


Having sought your opinions in my opening topic, I thought it only right to give my take on this which is much open to discussion. ok2


Enough from me as I have rambled on long enough!


Craig

Brigadair:
Hi Craig and all.




Clearly many variables, and no right or wrong answers because of this.


However, build it heavier rather than lighter in my opinion for the type of "off shore" racing on big inland lakes which we do. For the aforementioned reasons, along with others. Weight should be low as possible. C of g position from stern to bow obviously important, depending on boat, design, setup etc etc.




Most of the bmprs boats enjoying some success over the last 12 months, were certainly not of anorexic nature!!
Regards


Garry

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