Re-powering with a Beta Marine 14 - raw water intake?

[StuartWeibel]

I'm replacing a Yanmar 1GM10 with a Beta Marine 14. Existing raw water hoses, from the through-hull to the filter, and the filter to the water pump, are 1/2 inch (12mm). Beta Marine specifies 3/4" (19 mm) raw water hoses for their engine sizes 10 to 45 hp.

Given that the largest of the engines in this range is more than three times the displacement and power output of the Beta Marine 14, is it necessary to upgrade to a 3/4" raw water system?

3/4" (19 mm) hose cross section =~ 283 sq mm

1/2" (12 mm) hose cross section =~ 113 sq mm

If the cooling capacity of the raw water system is roughly proportional to the cross-section of the water column, then the smaller, 12 mm raw water system has about 40% of the capacity of the larger raw water cooler, while the power of the engine is about 30% of the largest engine for which 3/4" hose is specified by the manufacturer. It seems that the 1/2" should be more than adequate to cool the Beta Marine 14, or am I missing something?

I'd be grateful for thoughts from more experienced engine wizards than I.

thanks
stu

[Captsteve53]

Stu,

Definitely no choice there go with manufacturers recommended size (or larger!).

Why i say larger is that depending on your installation and the number of bends and or other restrictions (filters) it all adds ups to in reality how many gallons per minute you will pass through the pump, pumps starving for water will destroy impellers more quickly not to mention perhaps over heating with the engine (especially when running hard or heat exchanger gets a bit dirty/clogged).

If using bends in the systems try for ones that have a curve rather than a sharp 90 for instance.

In put from a NZ certified commercial Chief Engineer (35 years)

[Wotname]

Yes, I concur with Captsteve. Upgrade to 3/4" for all the reasons he stated.
It isn't about how well a perfect 1/2" system will work but how well a compromised 1/2" system will work compared to a compromised 3/4" system.

Adequate cooling water is as essential to the engine as clean fuel is; this is no place to go small. And if something does go wrong with your 1/2" system, all warranty will be denied.

The cost is marginal compared to the total cost of re-powering.