# Weight estimation of individual machinery components during conceptual design stage

Discussion in 'Diesel Engines' started by Venetia Tan, Apr 30, 2018.

1. Joined: Apr 2018
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### Venetia TanNew Member

Hi everybody,

I understand that in the conceptual design stage of a vessel, the lightship weight estimation is done for intact stability calculations. Also, i know that lightship weight estimation is divided into subgroups, mainly hull weight, outfit weight and machinery weight. However, im a student doing a journal paper focusing on the weight estimation of machinery weights particularly focusing on the weight estimation of the dry weight of the diesel engine itself. May i know what is the current practice for weight estimation of the dry weight of the diesel engine? When estimating the dry weight of the diesel engines, do you guys take the dry weight of the diesel engine from the manufacturer's catalogue itself or do you guys have a formula that could give you a rough estimate of the engine weight? Also, if only the total brake power needed to propel the vessel is known and the make, model and specifications of the engine are unknown, how do you guys obtain the dry weight of the engine? Any answers would be greatly appreciated.

Thank you.

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### TANSLSenior Member

There are many estimates that you must make before knowing the real values of many things. For example, you can not know the exact weight of the hull before calculating scantlings, but to make these calculations you should know the full load draft. The normal thing is to assume a draft of scantling and start calculating.
The same thing happens with the engine. You can assume a draft, calculate the displacement and make an estimate of the power needed for the speed you want. Once the power (approximate) is known, the best thing, imo, is to consult the catalogs of the manufacturers.

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### Venetia TanNew Member

Dear TANSL,

I understand where you're coming from. However, the project is on formulating an empirical formula based on the data collection of current engines which are available on the market. Although ship designers could consult the catalogs of the manufacturers, however, the objective of my project is to come up with a formula that ship designers could use for ease of calculations, instead of them having to constantly refer back to the catalogs. Hence, I was wondering what is the current practice. By the way, have you come across Watson's formula?

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### Venetia TanNew Member

New
Dear TANSL,

I understand where you're coming from. However, the project is on formulating an empirical formula based on the data collection of current engines which are available on the market. Although ship designers could consult the catalogs of the manufacturers, however, the objective of my project is to come up with a formula that ship designers could use for ease of calculations, instead of them having to constantly refer back to the catalogs. Hence, I was wondering what is the current practice. By the way, have you come across Watson's formula?

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### TANSLSenior Member

No, I do not know Watson's formula. I do not know if there is any formula that allows you to do what you need. In any case, those formulas (that were once very popular), if they exist, must be updated very frequently and, I suppose, vary a lot with the type of boat.
Honestly, and it's just my opinion, I would not trust those formulas very much. Another different thing would be to have a sufficiently large database and obtain, by means of regressions, equations that give us the installed power depending on the length, displacement or any other parameter that is considered appropriate.

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