Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

[barrythedude]

I have a great boat, love the merc, about 31MPH, 30 with two people, 28 or so with three. Once four ppl, I cannot plane for the life of me, just pushes water at 3MPH at full throttle. The motor always sounds like it is not revving where it should be no matter how many ppl.. My 1985 merc has a tach spot in front of the throttle arm body, is there a special tool to check RPMs, or can I use a plain old tach or prefereably a multimeter to check? I do use a hydrofoil and have tried to shift people around/only one tank full, etc. to no avail. I know 50 HP seems low for a 15'6" boat, but it is a modified trihull so the centre V is the main hull in the water at speed, the outside ones get out slightly. I may get a propulse prop, but hope you can just tell me what I may be missing or needing. Thanx guys!

 

[barrythedude]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

Doesn't anyone reply to these threads?

 

[hawghead]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

Patience dude, they will. That is a lot of weight for that 50 horse. Any rearranging of gear/people to get some weight forward would surely help. You say it has a Tach spot? You mean a gauge or a spot where a gauge would go?

They real knowledgeable folks are probably gonna want to know what your RPMs are WOT, the weight of the boat, the diameter and pitch of your prop. That will help them assess whats up.

 

[barrythedude]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

It is a 1986 so there is a tach "port" on the front of the throttle assembly by the steering wheel, not sure if I can wire any tach myself, or if I need an adapter. I am so worried because my old merc said a special tach/tool was needed or it would pooch the rectifier in the engine. That is what I was hoping ppl would answer for me. Pssst = thanx for your reply

 

[barrythedude]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

Plus, the boat weighs 830 kilograms (1870 lbs) with trailer and boat/motor, I figure 300 for the trailer (new metal welded for strength) so 1400-1500 lbs for the boat and motor.

 

[usskydvr]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

Ok let's get some terminology correct. The 'tach' port by the throttle assembly should be called the tach connection on the Controls. I have included one example for reference. You should be able to use any standard outboard tach for your engine.

 

[barrythedude]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

Nice graphics - thanx! My merc has the lockout on the top of the throttle and has the tach port on the front of the controller. You have to press a square button on the bottom to disengage the motor from the linkage to rev up the motor and warm it up. Seem familiar?

 

[usskydvr]

Re: Tachometer - Planing problems Merc 500 on a 15'5" Glastron trihull

Yeah, there are all sorts of configurations. I am familiar with the 'Commander' Series of controls. Send me your email in a private message and I can send you some other wiring diagrams. You can find the correct one.