How do insurance companys determine HP on older non factory (i.e. rebuilt/upgraded ) motors ? do they just go by what you tell em or do they show up with a propshaft dyno ? also how do they know how fast a particular boat is going to go ? again, do they just go by what you tell em or whip out a radar gun ?

on a lot of modern boat they have a guide to go by, tells speed with X amount of HP.

so your saying they go by what you tell then ?.... I really need some insurance guys to ring in on this , what if there arent any dyno sheets or other info to go by ? some dealers have no idea about the HP on used boats they are selling,or they just go by what the previous owner has told them,which w/out documentation is usually just sunshine they are trying to pump up your #@%& to sell you the boat (i.e. trade ins) im just trying avoid paying for insurance on horsepower I dont have

Some manufactures provide data on their models and different engine options to the insurance companies. The data includes HP & estimated top speed. Also, info published in magazines is used. True, the articles usually feature a boat that has very little fuel, no interior etc. The speed they publish is also taken into consideration even though your particular boat may not go that fast. Finally, the carriers have a "speed calculator". It uses speed & weight (along with hull type) to get an estimate on top speed. What you state is taken into consideration if reasonable. For example: If you had a 32' DCB with twin Ilmors in it and stated that your boat did 80 mph max, the carriers would call BS. You want to give your honest opinion on top speed to avoid an issue come claim time. If you honestly don't know the top speed, then say so.