20' CC Radar Question

[TooFly]

Shawt in the dahk here...

Does anyone have a radar dome on their 20? If so, did you need to increase the decline of the dome angle to compensate for getting up on plane or while running? I just had a top made for my boat and the fabricator put a 1 degree decline in it. He thinks that's be perfect.

Thanks,
Paul

[Old'sCool]

I do on my 23'

[Bushwacker]

Paul,

The Boating magazine test of a 20' Seafari I/O showed a running angle of 2.5 degrees at 19 mph, decreasing to 0.75 at 26 mph and 0.5 degrees at 31+ mph. The Seafari has more weight forward than the CC models, and the I/O CG is further forward than it is on the OB models, so both of those factors would make that test boat run a little flatter than yours. I think a 1 degree angle whould be about right at 25+ mph. Denny

[TooFly]

Thanks, guys.

Denny - Thank you for the solid data. I was planning on paying a friend's electronics guy to install everything because I'm afraid of messing up my new top. The install guy thinks I'm going to need a radar dome mount... without seeing the boat first. I'm puzzled by this. I told him that the fabricator, who made the top, said that the 1 degree angle down in the top should be enough and that the radar does not need a mount. Frankly, I think the electronics guy simply wants to sell me a mount. I'm not gonna lie. I do like the finished look that the mount gives the radar dome. But I question its "necessity."

Paul

[Islandtrader]

Originally Posted by TooFly

Shawt in the dahk here...

Does anyone have a radar dome on their 20? If so, did you need to increase the decline of the dome angle to compensate for getting up on plane or while running? I just had a top made for my boat and the fabricator put a 1 degree decline in it. He thinks that's be perfect.

Thanks,
Paul

Lets see if I can explain this to make sense. At rest take a level and mark a straight line on the side window(if you don't have one then on the gunnel)then run on plane, and take the level and mark your straight line again. The< should tell you the angle of the dangle...

Does this make sense?

[TooFly]

Yes, sir! Thanks man. I'll give that a try as soon as I can register the girl

Need a bill of sale first, dough. Ahem. ;0)

Paul

[BigLew]

Too fly,

What's the range of the radar you have or intend to use? What is its beam's angle? Does the beam's angle of transmission compensate for the planning angle? If so, mount it horirzontally and "don worry 'bout it!"

Ex. 4 beam degree angle divided by 2 is 2 degrees. If your planning angle is less than 2 degrees, don't worry about it. If its 4 degrees then use use a 3-4 degree wedge.

[TooFly]

Originally Posted by BigLew

Too fly,

What's the range of the radar you have or intend to use? What is its beam's angle? Does the beam's angle of transmission compensate for the planning angle? If so, mount it horirzontally and "don worry 'bout it!"

Ex. 4 beam degree angle divided by 2 is 2 degrees. If your planning angle is less than 2 degrees, don't worry about it. If its 4 degrees then use use a 3-4 degree wedge.

Thanks, BigLew. I haven't run the boat yet, so I don't know what my planing angle is. But the radar is a 48 nm Raymarine 4 KW HD Radome. Its horizontal beamwidth is 3.9 degrees.

Paul

[BigLew]

What is the height of the intended mount above sea level? Figure that 1/2 the 3.9 degree angle of the beam is 1.9 (or 2, for simplicity). Look at it as a right anlge triangle and figure the
distance out ahead of you that the beam hits the surface of the water. That will be the nearest distance your radar will show on the water surface. Check your trigonomety equations. Sine = opposite divided by hypotenuse, cosine = adjacent divided by hyponteuse, and tangent = opposite divided by adjacent. The angle value you use 1.9 degrees. The right traingle is 90 degrees, 88 degrees and two degrees. You should know the height of the radar dome (mounting height). Any problem ask a high scool student who has had trig!

Isn't 48 miles a little overkill for a 20' boat?

[strick]

Originally Posted by BigLew

Isn't 48 miles a little overkill for a 20' boat?

Not for this boat

strick