How to change the value of something when it touches a block? [UN-SOLVED]

So I've made a boat, and in the boats hull theres a BodyForce instance with Y axis set to 26500. Im trying to make this reduce to 13000 when the boat either touches a block or the Terrain, I tried doing terrain in general, but that wouldnt work as Im using roblox water for the sea. I needed it to only work when it touched the Grassy block from default roblox terrain...

I tried making a script that was in the ships hull, but I actually forgot to save the game, so cant provide that. I'm not the best scripter although did watch some of the videos provided by roblox. If someone could give me a push in the right direction, would be much appreciated. Thank you in advance! =)

Rays are able to return terrain and Parts

Try using this function that I made:

function CastRay(Object,Distance)
	local ray = Ray.new(
		Object.Position,
		Object.CFrame.lookVector*Distance)

local Hit = game.Workspace:FindPartOnRay(ray)
		return Hit
	end

BoatHull = game.Workspace.BoatHull--you dont need this
BoatHull.FrontSurface= "Motor" -- The motor represents where the ray is coming out from(you don't need this part)

while wait() do
--Example:
local Ray = CastRay(BoatHull,1)
	print(Ray)
-------------
	end

If you want it to work like the touch event make sure the distance is set to 1 like I did.

Have any questions about rays or anything else feel free to ask me.

Want to learn about Rays read these pages:

http://wiki.roblox.com/index.php/Raycasting

http://wiki.roblox.com/index.php?title=Scripting_Book/Chapter_17

I'll give you the start but not the whole thing because you could at least make an effort to make a script.

 game.Workspace.Boatpart.Touched:connect(function(Hit)
   end)

That's what I believe to be the start of that but I could be wrong, I'm a beginner scripter.