Advice - can this houseboat be made to sit level with extra buoyancy?

[bhnautika]

Here is a thought, if the boat weight is 4900kg and is deemed to to be over weight and you don’t put the allowed for 48 people onboard, only 8 saving approx 2800kg is the boat still over weight?

 

[fallguy]

Decks are designed, in general, to support a certain weight per square meter. Therefore, whatever the number of passengers, the maximum weight / m2 will be the same. In the case of people is 4 passengers (about 300 kg) per square meter, there is no room for more. And the dynamic loads generated by people moving when dancing, I do not think they are much greater than their own weight.

Yes. This is well known.

It would not need to be as large to accomodate a family of 4 if you are trying to reduce vessel weight.

Again, the OP said it looked like extra supports were added; not me. My guess is that it was originally designed for zero loading, or some lower headcount; despite good building practice of building for walking loads.

I said it looked rather large and the staircase is gaudy.

But this is all pot stirring now.

 

[fallguy]

Here is a thought, if the boat weight is 4900kg and is deemed to to be over weight and you don’t put the allowed for 48 people onboard, only 8 saving approx 2800kg is the boat still over weight?

The boat had lots of weight added to it. So much it didn't trim out on a test without loading passengers.

 

[fallguy]

And per OP was stern heavy. To what degree.

?

 

[bhnautika]

So what do we think would happen if the boat had level trim and you added the passengers who would be in the front half of the boat.

 

[fallguy]

So what do we think would happen if the boat had level trim and you added the passengers who would be in the front half of the boat.

The OP said it was stern heavy and overbuilt aft; not me.

Pretty obvious passengers for'd trim it out. That doesn't mean it'd be right if it is overweight.

 

[Sywofp]

Apologies for the long delay in an update - I have been away for work and was only able to meet up with the Naval Architect and go over his suggestions on the weekend.

He has modelled the boat and confirmed that with outboards and fuel, to sit with his recommend slight nose up trim that ~2000 KG of extra buoyancy needs to be added to the rear. Of course he is not suggesting to just add all of that with a hull addition - rather it would be a combination of removing weight, re-positioning some weight (especially the sullage tank) and adding buoyancy.

I had gone over the distribution of the weight added for the houseboat fit-out, and it's generally fairly even front to rear. But all those weights will be accounted for in the model before any changes to the hull are made, so it will float level as a houseboat.

And to clarify, I have said it is overweight at the rear, because of the trim, rather than a judgement about the overall weight. The Naval Architect does not seem to think it is overweight overall - just the weight distribution is not correct. After the modifications, the equilibrium trim is around 53mm (the bridge deck clearance between the hulls is 580mm). The equilibrium trim will increase 10mm for every 500KG added, so it is able to handle the houseboat fit-out without problems.

Basically at this stage we are refining the modifications and model for the modified boat. If the current owner is then happy to cover the costs of the modification for it to trim level (there will be some parts of the modifications that are at my cost too, in regards to it becoming a houseboat) then I will start looking at the best option to do that. Of course this would be subject to the work being done by a professional and the result signed off on by the Naval Architect.

I am being very cautious at this stage, so won't move ahead unless everything checks out. However I still think it is a unique and interesting boat that will make an excellent houseboat project, for a significantly lower cost than anything else I have seen that is comparable. There is a good chance though I think that the owner may not be happy at the cost to modify it (as this is currently unknown) and not want to go ahead, so we shall see.

But I have really appreciated the feedback, ideas and discussion here (so thank you!), and will provide some more updates as it progresses.

 

[fallguy]

So hull mods are required?

I am surprised.

 

[Sywofp]

So hull mods are required?

I am surprised.

Not so much required, as they are the suggested 'best' way (alongside weight re-distribution and removal) to get the boat at the ideal trim.

The Naval Architect is not concerned by the overall weight, just the weight distribution. One thing I forgot to mention is that after correcting a mistake I made with the measurements, as well as some more accurate measurements of the exact waterline now it's back out of the water (there is a very clear line on the hull) the boater is lighter than I originally thought.

So it's a 3970 KG, not 4900 KG. There without doubt sections that are overbuilt, especially for my purposes. But considering the size of the boat it's apparently not too bad, and has plenty of reserve buoyancy for my purposes as long as the houseboat fit-out weight is carefully track and modelled.

I can absolutely see the value, and appeal, in stripping out the rear of the boat and rebuilding it lighter, and with a better weight balance. But I can also appreciate that it will be time consuming and costly, and not something the owner will be willing to do, and not something that is affordable for me to do.

If I don't buy it, the owner will no doubt make the modifications suggested by the Naval Architect and sell it to someone else.

At the end of the day, I am not too concerned about things like the large, enclosed stairs, as they are very practical, despite being overkill.

What I am asking myself is, am I interested in buying the modified boat? Sure, a design that has been modified and re-purposed is not ideal, but if the design is done by a naval architect, and it's properly built, what are my downsides compared to the original purchase?

A lighter, sleeker boat would be nice. But those wide heavy stairs will come in handy for the two great danes my wife and I want

 

[bhnautika]

Sywofp good luck with your new project if you go ahead.

 

[Sywofp]

So, a disappointing update. The short version is I pulled out of buying the boat and got my full deposit back. Thanks to everyone who gave me feedback and suggestions.

The Naval Architect and I worked out an addition that involved removing the central pontoon, and rebuilding it much larger (with a deeper draught) as well as making some minor changes to the rears of the side hulls.

I presented the changes to the owner, and tried to work with him to make it happen, but he was not interested (as is his right) beyond a small contribution to the cost. The quotes I got for the work meant it was not going to be economical for me to have done by a third party, and aluminium welding is not a skill I posses, so I pulled out.

The owner has another guy interested anyway, so the sale cancelation was all perfectly amicable. I wasted a decent amount of time, but learnt a lot so I am not too worried.

 

[fallguy]

Best of luck to you. I personally would have done all the work above the hulls, but I understand the reservations about adding work to a purchase and I know zilch about the asked price. Thanks for finishing the circle. Lots of these stories never get updated.