trim problems chris craft 21ft bow rider - V6 4.3ltr

[coast108]

I looked in the other topics but couldn't find the info I need. Forgive me if this has been discussed earlier please.

The boat is taking ages to come flat on the water with full power and prop trimmed vertical.

Can't move gastank to the front etc. Prop has been replace with a better pitch to give it more pull by a
specialist.

I have been looking at trimtabs. The ones with full control are somewhere around Euro 1,500 here in holland.

There is also a more economical version they call smart tabs. Anybody with experience with those?

Also how can I calculate what smart tabs I would need for my boat in view of pressure needed on the
springs in kgs?

Most important to know is whether this could solve my problem as with the way it is now the boat is
dragging for a long time before it planes. Think minutes not seconds.

Appreciate all the advise I can get.

Thank you,

Brgds,
Ton

 

[tpenfield]

What does "prop trimmed vertical" mean . . . .?? I assume you mean in the full or nearly full down position? If so, is the bottom clean? Carrying any extra weight in the hull, like water weight ?

 

[coast108]

Hi, sorry for my poor english in this matter.

Indeed I mean full down position.

Hull is clean.

We have a water bag lying in the bow underneath the seats which is presently empty. Going to
fill it up tonight hoping it helps a little bit but it is only 75 ltrs i.e. 75 kgs.

 

[Scott Danforth]

your boat should have a great hole shot without trim tabs

here are a couple of items that may cause poor performance:
poorly adjusted throttle cable
not running on all cylinders
incorrect timing


I would first make sure it is running on all 6 cylinders. I have encountered many motors running with one or two dead cylinders that seem to run well, however are down on power.

I would start by doing a power balance test - pulling one spark plug wire at a time, and watching the RPM's when you pull one that doesnt change the RPM's that cylinder is not contributing.

follow that up with a compression test.

also, if you have an exhaust flapper that has dropped down, it will restrict exhaust to the point of restricting power.

 

[coast108]

thank you for all your responses.

engine is running on 6 legs. compression is also good. was checked last week by a mechanic familiar with
OMC engines which is not too common here in the Netherlands but finally we have found one and even close
to the marina. Engine sounds regular. We got her back only yesterday from the shop. 9 out of 10 mechanics
here won't even look at an OMC engine which strikes me as odd as it are all the same engineblocks. But
it is what it is.

++++

- poorly adjusted throttle cable.

you mean that we might not be able to give full throttle?

- exhaust flapper

never heard of that. just googled it and understand what you mean. will have to look for it tonight. I was
of the impression that the exhaust came out somewhere near the outdrive underwater.

I remember from last night that the engine was running at around 5,000 RPM which if I am not mistaken
is what it should be. (OMC V6 4.3ltr)

Thanks

 

[coast108]

thank you for your responses.

engine is running on 6 legs. compression is also good. was checked last week by a mechanic familiar with
OMC engines which is not too common here in the Netherlands but finally we have found one and even close
to the marina. Engine sounds regular. We got her back only yesterday from the shop. 9 out of 10 mechanics
​here won't even look at an OMC engine whic

- poorly adjusted throttle cable.

you mean that we might not be able to give full throttle?

- exhaust flapper

never heard of that. just googled it and understand what you mean. will have to look for it tonight. I was
of the impression that the exhaust came out somewhere near the outdrive underwater.

I remember from last night that the engine was running at around 5,000 RPM which if I am not mistaken
is what it should be. (OMC V6 4.3ltr)

 

[KYsean]

What pitch is the prop you have now? How many blade?

 

[coast108]

Hi, 4 blades. not sure of the pitch. will have a look and revert.

We filled the water bag in front of the boat and she was coming out of the water much easier, now a matter of seconds which is a big step forward.

we are getting about 4,000 rpm's. do you know whether that is sufficient for this engine? full speed was logged last night with gps at 50 km's.

if one says "mph" in order to convert from km's. is that bss landmiles or seamiles? Yesterday I got a note from someone out of Canada with
same boat same engine with a topspeed of 43 mph. guess it is landmiles but that still equates to roughly 70 km an hour.

reverting with pitch soonest.

Thank you for your interest.

Brgds,
Ton

 

[southkogs]

50kmph is about 31mph ("land" not nautical miles). Nautical would be about 26kts.

All of which are a little slow for your boat. I would think that's a 40MPH / 60KPH / 35KTS boat. RPMs sound low. I like Scott's ideas above, particularly checking your throttle cable. It may be as simple as your throttle isn't working right. Though prop pitch can do that too.

Welcome aboard Ton.

 

[airdvr1227]

I might have missed it but you don't say how old or how many hours but if its an OMC setup it must be getting up there. I had an older Chris Craft boat that was just tired. Wide Open Throttle should be closer to 4600-4800 RPMs and your top speed should be more than you are currently getting. I am guessing you are 'over-propped'. Tell us the current pitch and we'll probably be able to get you closer to the RPMs you should be seeing. Also, is this boat new to you? Did it ever run better than it is now while you owned it?

 

[coast108]

Hello Scot,

Thank you for your reply.

We purchased the boat last season off the internet. Big mistake as it proved to be.

We only had problems sofar till couple of days ago when for the first time we were able to
sail with the boat for over one hour without stoppages. Tuesday was the first time we were not towed of the lake.

Boat and engine (OMC sterndrive and bravo outdrive) are both from the late 80's. We liked the shape of the
boat together with here beam of about 2.60 mtr. Next to that she has a coastguard plate in it with an american flag on
the sides which looks nice. We didn't looked any closer. Rookies mistake I guess. We did not even noticed
that they spelled "limited" as "limeted" judging a book from his cover......

We spend a lot of money on mechanics already and we seem to be getting there slowly but surely. You said
that the boat might be tired. I was off the same feeling last season and for that reason I had the compression
tested which came out ok. Any other way to figure out whether the engine is tired?

Will get in the water this weekend to find out what pitch we have.

At the moment she is running better then she has since we got her.

Brgds,
​Ton

 

[coast108]

Good day,

This is what is mentioned on the prop "Vortex IM Wheel - 992202 - 15x16 (or 15/16 can't recall)"

Picture attached is from the carb (Holey) I have been told to take of airfilter and look into the
carb to see 2 or 4 barrels. Can somebody tell me whether this is a 2 or 4 barrel carb as that
2 of the 4 holes are covered with some sort of little plate possible to give direction to the inflow
of air.

apparently this would make the difference whethre we have 175hp or 205hp to play with.

at full throttle the engine does max around 4,000 RPM. in neutral the engine does easy
5,000 RPM.

Pleased to hear,

Brgds,
Ton

 

[Chris1956]

Looks to be a 4 barrel carb. It therefore should be 205HP. I have had that motor in an 18 foot boat, which was lighter than your boat. 42MPH was about all the speed I could get out of it. Power trim tabs helped to get her on plane with a heavy load. They will help you, I would guess. You will want a prop with the pitch to allow at least 4500RPM at full throttle, with the motor trimmed some, and a normal load.