bow digging

[90Evinrude]

i have a 72 winner 15ft runabout with a 90hp. Wide open the boat bow digs like crazy i am wondering if it is poor hull design or is the motor to big for the boat, the boat is rated up to 80hp. i have no idea on this matter so any help would be great .. Thanks

 

[scipper77]

Re: bow digging

Digs? Do you mean it is not getting up on plane?

The standard responses are going to be things like make sure you are trimmed properly and where is your anti-cavitation plate?

 

[scipper77]

Re: bow digging

Other things to check are: is the prop correct for the setup and what are your WOT rpm's

 

[kahuna123]

Re: bow digging

And probably what is wrong looking at the age the hull is hooked. Sitting on a roller trailer with the last wheels a foot from the transom. Bad stringers and so on.

 

[90Evinrude]

Re: bow digging

the boat planes fine but once u get to 3/4 throttle the front drops and starts digging into the water on semi rough days and i lose a good 7-10 mph and the prop is correct and i cant tell you the rpms as i dont have a tach the motor is 100% with no problems and on any trim level still digs. the more weight in the back the better it rides as its lifts to bow up a little and anti-cavitation plate is fine and straight im seems as if either to hull is poorly designed or the motor has to much power for the boat

 

[90Evinrude]

Re: bow digging

the boat planes fine but once u get to 3/4 throttle the front drops and starts digging into the water on semi rough days and i lose a good 7-10 mph and the prop is correct and i cant tell you the rpms as i dont have a tach the motor is 100% with no problems and on any trim level still digs. the more weight in the back the better it rides as its lifts to bow up a little and anti-cavitation plate is fine and straight im seems as if either to hull is poorly designed or the motor has to much power for the boat

 

[90Evinrude]

Re: bow digging

boat was on a float on trailers and during the last 3 winters has sat on a wooden dolly with supports on the front middle and back with no over hang and was supported to sit sraight and not on any angle

 

[oops!]

Re: bow digging

there ate two possibilities for this.

a hull hook (not very likely)

or the motor is in the incorrect position.
there are several trim pins that adjust the angle of the motor on the back of the boat...chances are....it is adjusted wrong.
when the boat is on the trailer....have a look at the motor in relation to the hull, with the motor in the full down position...the motor should be parelell with the transom of the boat.....(this is a rough way to tell)
the anti-vent plate should be a continuation of the hull. any angle up or down will cause either porposing or a hull dig.

to check for a hooked hull take a string line and run it from the flat part of the keel to the end of the keel......(do the same on the lifting strakes as well)
there should be no space between the string and the hull. if the string touches the hull so the hull is bent in a kind of smile....that is called rock.
if there is a space....its hook.

 

[oops!]

Re: bow digging

btw....it has nothing to do with the motor being too big for the boat.....you could drop twin 300 e-tecs on it and if installed correctly....it would not do what you are sayng.

 

[chriscraft254]

Re: bow digging

Is there trim tabs on this boat? Dol- fin? Do you have tilt on the motor? Trim tabs that are stuck in the down position can cause this at higher speeds. Dol- fins can also cause the boat to pitch bow down at high speed if you don't have the ability to trim the motor. Can you trim the motor to bring the bow up or down? Need more info, pics of the boat might help also. The difference between a 80 and 90 hp motor isn't going to make a difference.

How do you know the prop is right, if you don't know what rpms you are getting? The prop could definately be the culprit.

 

[90Evinrude]

Re: bow digging

i will check these things out as i wanted to get a general idea of what the problem may be. Thanks

 

[90Evinrude]

Re: bow digging

their are no tirm tabs , yes their is a tilt motor tirming up brings it up a bit but it still digs , the skeg is also missing a big piece, the prop is a little beat up but the motor ran like a top and never had any problems.. but i am not sure about the rpms you could def be right . Unfortunately the boat sank about 3 weeks ago and unless i decide to rebuild the motor from top to bottom which might not be worth it .. i am going to look for a another 90hp i just kinda wanted to get a idea of what the problem may be as this was the second motor on the boat and they both made the boat dig

 

[scipper77]

Re: bow digging

Could this be cavitation?