Lobster Boat - too much pitch and roll

[shorelinedesign]

I have a 1957 Lobster- Style boat (Mascot) - 22' LOA. It is a great boat and will take 4' seas head on, but look out in a following sea. I have had her 12 years and rebuilt the upper structure. I have always thought about adding trim tabs or widening the chines, but am unsure if that would help or hurt. The bottom is rounded like a sailboat. Does anyone have any suggestions for reducing the roll?

[wdnboatbuilder]

What happens in a following sea? And are you under power?

I'd add more keel...

More weight down low to stiffen her roll period. Also - more directional control in a following sea.

Looks a lot like a family boat we had when I was a kid that my dad built. Fremantle naval architect Randel design from memory...18 ft bondwood strips in 3 directioanl layers and skinned with woven rovings and resin.

Just love the look of these types of hull.

Cheers

[h_zwakenberg]

did it behave like that before you added the superstructure? If not, your additions shifted CG too high up, with the consequences you noted.

If sea behavior was sound before those additions, consider the following:
Before resorting to trim tabs, chine modifications and other 'tricks' that don't heal the cause of the problem, first check whether you can lower CG. That way, your hull will remain cleaner...

bye
Hans

[shorelinedesign]

Originally Posted by wdnboatbuilder

What happens in a following sea? And are you under power?

The boat tends to roll down the wave face, requiring significant full rudder turns in each direction to keep it upright. It feels like she wants to roll over if you don't counter steer. That was in about 3' to 4' following seas, which is not a normal condition on the Chesapeake Bay, but it does happen. But even in smaller following seas, it rolls significantly.

[shorelinedesign]

Originally Posted by trouty

I'd add more keel...

More weight down low to stiffen her roll period. Also - more directional control in a following sea.

Looks a lot like a family boat we had when I was a kid that my dad built. Fremantle naval architect Randel design from memory...18 ft bondwood strips in 3 directioanl layers and skinned with woven rovings and resin.

Just love the look of these types of hull.

Cheers

The hull is all fiberglass - believe it or not for 1957! It is a heavy boat, maybe 1/2 inch thick glass. I like the idea of adding more keel, especially considering that replacing the aged keel has been on the to do list. Do you suggest a thicker and-or deeper keel?

[shorelinedesign]

Originally Posted by h_zwakenberg

did it behave like that before you added the superstructure? If not, your additions shifted CG too high up, with the consequences you noted.

If sea behavior was sound before those additions, consider the following:
Before resorting to trim tabs, chine modifications and other 'tricks' that don't heal the cause of the problem, first check whether you can lower CG. That way, your hull will remain cleaner...

bye
Hans

I am sure that the CG was shifted higher. The previous roof line was about 3 inches too low for our 6'2" frames. The structure is also built on a heavier mahogany frame. However, the rolling problem existed prior to the roof replacement and is now maybe slightly exacerbated.

[water addict]

Maybe a simple solution would be to remove that heavy looking canopy and replace it with a canvas bimini that would give the same shelter but be a fraction of the weight. Then you would have no changes to the hull, and your boat would be lighter, stiffer, and get better fuel economy.

with the keel moreso than wider...yes wider will give you weight below the metacentric height and improve roll period, but it won't give as much directional control as a deeper keel in a following sea - the deeper keel gives both (but reduces draft!) Theres always a tradeoff - isn't there!

You know - what you describe is very common on round bilge vessels with a long roll period.

It takes a LOT of experience / practice / understanding, NOT to oversteer them...

Think about it, what effect does turning the rudder have when the boats heeled well over?

Yep - it either lifts or lowers the bow (just like a trim tab, which is exactly what a trim tab is - a rudder turned on it's side!)

So - when you THINK your countering a turn with helm by oversteering - your doing no such thing - your alering the bow trim - not changing direction.

Best to alter direction by making helm (direction) adjustments at level heel, and just hang on in the heel / roll...until she rights again....

Everyone who hasn't steered a long roll period boat (that heels well over) - makes the obvious mistake of oversteering initially - it just takes time to get used to how your boat handles, is all.

Correct course at mid roll i.e. when the boats upright - not after it's heeled...or your just making trim tab adjustments with your rudder...which may or may not help the loss of directional control feeeling...(and may in fact make it worse!).

Hope that makes sense - maybe someone can explain it better than me!

Cheers!

[cyclops]

I am not to sure you would want to be hitting up and down trim buttons at the same time you are turning the rudder and watching out for the doubledecker wave also. Very tiring after a few minutes. Go for the larger keel area and a larger rudder area. Those 2 together will absolutly reduce the the swamping risk to a minimum, reduce the speed and amount of rudder swing. The large rudder swings slow the boat down. We want the boat to maintain enough foward speed to have a + or almost positive foward speed. The 2 changes will make her a pleasure in a mandatory travel in following waves.---------------------- Correction. Always drop the anchor if it gets hairy. Hopefully, your anchor can cut thru seaweed beds and then dig in.------------------------------ Then there is always going to the quieter downwind side of a island and saying, " MOMMY ".

[safewalrus]

Don't overestimate you or your boat! Take a couple of bags of 'beach' as ballast if you need to lighten they can be dumped without to much hassle or cost and don't run unless you have to! running will always produce some rolling! (that'll get 'em going) the trick is to reduce it, more power OR tow a warp (sea anchor) or like cyclops said 'discretion is the better part part of valour' get down behind that island! Prudence ain't being chicken it's "good seamanship"

[shorelinedesign]

The canopy is heavy, but I really like it. Besides, the rolling effect was present before the new canopy was installed.

I like the longer keel suggestion. What do the naval architects think about the keel? It needs to be replaced anyway - it's partially cracked through at the skeg/rudder connection.

[cyclops]

Could you navigate to your old places with a 6" deeper keel? A keel is what makes EVERY SINGLE engine boat a pleasure in bad weather.-----------I am not a N. A.------I automaticaly add deeper keels to any boat that waddles too much.

[shorelinedesign]

Everyone - Thanks for your time and ideas. Wish I had asked sooner.

Cyclops - six inches added draft should not cause any problems. Would such a change require modifications to the rudder and drive shaft - or do would you taper the keel down to its present design? Since this is a project you have apparently have great experience with, I would appreciate any further details.

Thanks - Wes

[cyclops]

I am not qualified to design other peoples boats. I only have learned what can help some problems. BIG difference.