Rolly custom steel motorboat

This method might also be useful for estimating the roll period?

bajansailor said:

This method might also be useful for estimating the roll period?

Click to expand...

Thank you. It might be tricky to do this alone on my boat with larger volume, but worth to try. Any data is helpful, even if it is not highly accurate.

I messed around with the App on my tablet and I have some results, but not the way I wanted. The App does not allow graphical recording, only data in CVS format. I took screenshots of the rolling process, but it covers only sections of it.
I rocked the boat myself from the dock. I also started a stopwatch to measure the length of time, until the boat calms to almost no rolling. This took about 55-65 seconds.
I attach photos of the App shots. The X line looks the same, but the Y axis number changes.
I will try to get something better, but I just wanted to illustrate what this App can do.

Interesting to see how robust the ' twin keels ' are on this solid passagemaker. I suspect, it will have to be similar on my boat, but much larger due to the volume of my boat.

bajansailor said:

This method might also be useful for estimating the roll period?

Click to expand...

I did a roll test. Measured it several times and it was mostly the same.
- average roll time for one full roll = 6.5-7.1 seconds
- beam 14.2' = 4.32 meters
- freeboard 4' = 1.2 meters.

Not much stability, but we knew that already. Although, the table above does not include these sizes.

LeoKa said:

Not much stability, but we knew that already. Although, the table above does not include these sizes.

Click to expand...

If I try to extrapolate upwards by following the general trend of roll periods versus beam and freeboard, I estimate that for 4.3 m beam and 1.2 m. freeboard, the maximum roll period for adequate stability is about 4.9 (say 5.0) seconds - which is still a fair bit less than your 6.5 - 7 seconds.

bajansailor said:

If I try to extrapolate upwards by following the general trend of roll periods versus beam and freeboard, I estimate that for 4.3 m beam and 1.2 m. freeboard, the maximum roll period for adequate stability is about 4.9 (say 5.0) seconds - which is still a fair bit less than your 6.5 - 7 seconds.

Click to expand...

I believe you are correct. I definitely need some type of modification.

I am searching for boatyards in my vicinity now, who does design and fabricate/install twin keels on metal boats. Most of the yards here in the Portland, OR area are non-metal boats oriented. If there aren't any who can haul out a 54' boat, I will have to look further out, closer to the ocean. Astoria, OR has welders, but not designers. Same in Ilwaco, WA. I have been to one commercial yard a while ago in Charleston, OR but they are 4-5 days sailing from me. Finally, there is Puget Sound and B.C. where there are several places who could do this for me, but that should be my final choice.

The modification I want is what Ad Hoc suggested earlier. Cut off the air tank at the stern and mount a pair of keels to the hull. (three-keel?) My boat had bilge keels at one point in the past, but either it did not work well, or it was unattractive to the previous owner and it was removed. The version I imagine is not going to be bilge keel, but rather twin keels, as they are used on sailboats. Meaning, it will be mounted right below the bilge level, but will be long enough to beach the boat, if needed. It can be fairly easy to fabricate one, as long it is not hollow, but it is one thick sheet of metal. I wonder if it was a 3/4" sheet, how much weight would it add to the lower section of the hull? I do not have solid numbers, but it should be at least 4-5feet long and 3-4 feet deep, plus a shoe at the end of it and a base plate at the hull for mounting enforcement. If that weight is not enough for lowering the COG of the boat, I will need to add lead ingots to this keel on each sides, gradually to watch the trim, as Ad Hoc recommended. The removal of the air tank will restore the original hull shape as it was designed, but also I will loose few thousands pounds of weight. So, adding weight to the keels might be necessary. However, if the COG is lowered this way, I think my boat will behave better.
I am not looking for perfection, of course. My boat will never be ideal. However, if the stability can be improved a bit with these modifications, I want to do it.

LeoKa said:

... The version I imagine is not going to be bilge keel, but rather twin keels, as they are used on sailboats. Meaning, it will be mounted right below the bilge level, but will be long enough to beach the boat, if needed. It can be fairly easy to fabricate one, as long it is not hollow, but it is one thick sheet of metal....

Click to expand...

You need to be careful that one thick one, will not buckle, when used as a beaching keel, from any minor offset loads when beaching, and also the weld to the hull has sufficient weld length to overcome the loads + fatigue + corrosion.
That's where a "hollow" as you're calling bilge keel, is better - it is way stiffer.

Ad Hoc said:

You need to be careful that one thick one, will not buckle, when used as a beaching keel, from any minor offset loads when beaching, and also the weld to the hull has sufficient weld length to overcome the loads + fatigue + corrosion.
That's where a "hollow" as you're calling bilge keel, is better - it is way stiffer.

Click to expand...

I see. I have a feeling that you do not recommend the single plate version for my boat? I suspect you have a reason for saying it and believe you.
I thought it would be easier to cut out a single plate, a thick one, and weld it on. Can a single plate version have a support section added?
The bilge keel requires designing, which I cannot do.
Even the single plate version is a week long job for the welder I spoke to two days ago, when I went to see him at the yard where I have the haul out in August. He told me that the keel will be at least a week work, and the blip cut off another week. That is a lot of labor hours. I do not know much about this project, so I just had to take his word for it. When I suggested to cut out and assemble the keel ahead, before I haul out, and just weld it up, when I am there; he was not very enthusiastic about it.
Originally, this was my idea. Fabricate and assemble the keels off site, deliver them when the boat is on land and mount it. I had a feeling that he was not very confident about this project. It is not what he is normally used to.
For pre-fabrication, I will have to get sufficient drawings of these keels, before I can hire someone to weld it together. Regardless, if it is a bilge keel, or a single plate version on the photo.
I also went to a commercial yard, close to my marina. They work on all type of vessels. They have designer, welder, all labor for a job like mine would need. When he come up with a 250K estimate for my order, I realized quickly that I was on the wrong place. Maybe he just wanted me to walk away, so he scared me with that number. He succeeded.

Ad Hoc.

Do you think it would the best just to put back the rolling chocks to the same place, where it used to be? Maybe make it thicker and heavier to compensate for the blip removal weight? The rolling chocks would not serve as beaching keels. Just rolling reducer and weight addition platform.
Based on the photo, where I can see the welding of the old rolling chocks, it could have been about 6-9 feet long. I do not know the thickness of the chocks, nor the length. If the new chocks were thicker and wider, will they serve the purpose of anti-rolling/weight balance?

LeoKa,

I have just reread all your posts here.

Quit while you're ahead.
Sell the boat as is and move on.
Buy what you want, something that better suits your needs.
Smaller, cheaper, better.
A boat you like to be on and to sail ( motor ).

You could spend thousands and waste a ton of time only to have similar results.
Look at all those before you that have tried to "fix" your boat.

Buy a proven design that you like and that fits your needs.
Any idea what boat that might be?

Cheers

BlueBell said:

Quit while you're ahead.
Sell the boat as is and move on.

Click to expand...

It might happen. We'll see.
Thanks.

LeoKa said:

It might happen.

Click to expand...

What boats are you considering?

I take it you're in Vancouver Washington?

Thanks

Yup, you must be in Vancouver Washington.

No other boats tickle your fancy...?

BlueBell said:

No other boats tickle your fancy...?

Click to expand...

I am not sure why you keep asking me about another boat? I am not interested in other boats.
Are you a broker?