# Stability Problem



## dundalkie (Mar 15, 2006)

A friend of mine is proposing to place a new wheelhouse unit on a 1950s built former naval harbour service boat. The boat is about 60 ft long by 15 ft beam. The wheelhouse is steel framed with teak panelling and glass windows. My query is would this wheelhouse affect the stability of the boat bearing in mind that the boat has been stripped out and is lighter than she would have been in service. Also what should be considered before the wheelhouse is mounted?


----------



## Keltic Star (Jan 21, 2006)

Without any doubt it will affect the stability. He should use the original stability booklet to deduct the weight of everything that has been removed and then add the new house and related fittings and recalculate the weight and longitudinal and vertical CG's for each item. 

If the original stability booklet is not available, an inclining experiment will be required after conversion to calculate the new stability conditions but this is after the fact and then too late to correct.

If the original lines plan is still available a computer model can be created which can provide a new stability booklet for given conditions. Today, this is the cheapest method for small craft conversions. If there is no lines plan, a more difficult and expensive method is to physically measure hull offsets to create a new lines plan. 

The accuracy of the results are fully dependent on the owner (builder) inputting accurate information in the first place. One of the biggest problems with yacht stability is "creeping weight" which is everything added on board since the boat left the builders yard and therefor has not been considered in the original stability margins and successive owners have neglected or forgotten to keep accurate records.


----------



## dundalkie (Mar 15, 2006)

Thanks keltic Star. It looks like a lot of research is in order here. No stability book is with the papers. have to see what will hapen from here.


----------



## Derek Roger (Feb 19, 2005)

Notwithstanding Keltics answer ; if you construct the wheelhouse in the same materials and dimentions as the one you are going to demolish the stability will be more or lesss the same as you now have . A lighter construction would improve the exsisting stability .
You could perform a roll test before and after the work and establish stabity in that way which is cheaper than an inclining experiment ( have it done by a Naval Architect ) Worst case would be to have to add some permanent ballast .


----------



## Stephen J. Card (Nov 5, 2006)

dundalkie said:


> A friend of mine is proposing to place a new wheelhouse unit on a 1950s built former naval harbour service boat. The boat is about 60 ft long by 15 ft beam. The wheelhouse is steel framed with teak panelling and glass windows. My query is would this wheelhouse affect the stability of the boat bearing in mind that the boat has been stripped out and is lighter than she would have been in service. Also what should be considered before the wheelhouse is mounted?



If it is a 'new wheelhouse' can we assume it is replacing an existing structure? If only the frame is steel the additional weight it may not be so critical... the panelling and windows replacing something of similar weight. Consider making the framework out of aluminium insteaad of steel. I would suggest inviting a nautical surveyor in your area to have a quick look at the situation before taking any drastic or costly steps.

I remember an old R.N. Duty Diesel Boat here in Bermuda that was built in the UK and was here for many years. About the same dimensions. Vertical stem, counter stern, built like a battleship. The deck casing and funnel was steel but the small wheelhouse was wood and open at the back. I wonder if yours might be the same basic design. These boats could easily carry fifty or so chaps sitting about the upper deck. 

Have a look in the photo Gallery under RMAS HARBOUR LAUNCH. Is this the type of craft you are taalking about?


Stephen


----------



## John Cassels (Sep 29, 2005)

Derek , why use a surveyor ?. Not all that difficult to carry out a good estimation using the rolling period.


----------

