A question of maintaining/changing raw water hoses came up the other day. Be assured that they can and will go bad at some point. nothing last forever. Stella blue was about 12 years old when these photos were taken of the main engine raw water intake hose. The original equipment hose was Trident wet exhaust hose which is made in Turkey. That hose did not fair well. The same hose but smaller diameter was also used for the genset. I replaced that one at 8 years because it was shot. 
As you can see the wire coils are rusting away to both sides of the hose. It looks like a poorly made hose to me.
When I replaced the genset hose I used Bellowsflex, Made in the USA and a much higher quality of hose. The great part is it is cheaper than the Trident hose when you purchase it from an industrial supplier. I purchase my hose from Cut & Couple online at http://www.cutandcouple.com/index.html
As you can see, it is approved for wet exhaust, raw water, and fuel. It is a far superior hose to the original Trident hose.
The hose between the through hull and the seawater strainer is 2". The hose between the strainer and the engine was also 2" but intake on the Yanmar engine is 1 3/4". Mainship used 2" hose and clamped the cheap hose down to make it work. When using a beefier hose like the BellowsFlex, this will not work. the hose will not collapse around the smaller intake fitting enough to seal. Change the fitting on the strainer and then use 1 3/4" hose for that run.