89 300 Weekender

[ks65609]

Now that we are proud owners of a classic it makes sense to move to the proper forum category..

Thanks to andyr for the help.

This is our first experience with a larger twin engine boat and I must say we are very happy with our purchase. Lots to learn. Neighbours at the marina have been very helpful although all have newer stern drive units. Most are surprised to see a 30 ft boat with twin direct drive big blocks.
As I was told, the handling and manuouvering in tight spaces is awesome and the boat will turn basically in its own length. Very stable boat that holds course very well once trimmed.

A few questions :

RPM/Speed
I have always used an rpm/speed ratio when adjusting trim, as well as engine sound and the general feel of the boat to find the " sweet spot " on plane. I am finding with this boat about a 300/400 differential. For example, engine rpm of 2800 and gps ground speed of 23 to 24 mph depending on water conditions. I also find that a higher rpm of 3400 will produce a gps ground speed of 31 mph. I was wondering what others' experience may be. I understand this is not a proven technical approach but it seems to work. I am running twin 16 x 17 counter rotating props. I have not gone to WOT and do not desire to however would like to know what the max rpm should be. I am guessing 4200 to 4600.
Bow stanchions
How are the bow stanchions identified. Example, #1 stanchion starboard side. I understand the stanchions are through bolted however so far cannot find access to the under deck backing plates/locking nuts.
Raw water pump impeller
I would appreciate information on the procedure to change the raw water pump impellers. The pumps look to be self contained v-belt driven with a supply hose from the sea-cock strainer and an input hose to the engine, both attached to the rear of the pump. It appears to me the entire pump should be removed from the engine and serviced and possibly one or two of the batteries removed to provide elbow room.
Carb secondaries
I have been advised the carburetor secondaries kick in above 3000 rpm and would like to know if this is correct. The run I did at 3400 rpm just seemed to be where the boat was meant to cruise. It was smooth, and engine sound was good.

Thanks for your help and patience.
Ken

 

[SCORPIO]

I don't know if they are identified at all other than to say 'port foreward bow stantion, or second one back on the port side' . On my 89 300DA the bolts and cap nuts are above the headliner. You need to feel along the outside edge under where the stantion is and you will feel the cap nuts. Some are inside the built down sections of the galley and over the dinnette. You will need to carefully cut the liner to gain access to them if you intend to remove or rebed the stantions.

You should be able to hear when the secondaries start opening, there is a pronounced change in the sound of the air rushing into the carbs. Mine start to open around 3200 or so. I have fuel flow meters and when I see the numbers start to rise above about 12-14gph I back off a bit and cruise just below the secondary opening point.
My boat has outdrives so I cruise at a lower rpm than a boat with inboards. You may have to get into the secondaries a bit in order to keep the boat up on plane due to the angle of your shafts relative to the direction of travel. Play with the trim tabs too to optimize your cruise so you can stay on plane at lower rpms.

WOT should be 4200-4600 as you already stated.

 

[ks65609]

I don't know if they are identified at all other than to say 'port foreward bow stantion, or second one back on the port side' . On my 89 300DA the bolts and cap nuts are above the headliner. You need to feel along the outside edge under where the stantion is and you will feel the cap nuts. Some are inside the built down sections of the galley and over the dinnette. You will need to carefully cut the liner to gain access to them if you intend to remove or rebed the stantions.

You should be able to hear when the secondaries start opening, there is a pronounced change in the sound of the air rushing into the carbs. Mine start to open around 3200 or so. I have fuel flow meters and when I see the numbers start to rise above about 12-14gph I back off a bit and cruise just below the secondary opening point.
My boat has outdrives so I cruise at a lower rpm than a boat with inboards. You may have to get into the secondaries a bit in order to keep the boat up on plane due to the angle of your shafts relative to the direction of travel. Play with the trim tabs too to optimize your cruise so you can stay on plane at lower rpms.

WOT should be 4200-4600 as you already stated.

I was not sure how to identify the stanchions as the # 1 starboard needs rebedding according to the survey. Now I know it is the first one from the bow. I have felt around the cabin liner but must not be looking in the right spot.
I do not have fuel flow meters and I will listen more closely to the air intakes. With the inboards the are right below where I stand. Are fuel flow meters fairly simple to install ?
I am continuing with small adjustments to the trim tabs to find the sweet spot. With previous i/o units I have owned the difference between rpm and gps speed was in the 500 to 600 range consistently whereas with the direct drive set up the difference seems to be much smaller. The previous owner suggested almost a one to one relationship. The fuel flow rates I have been advised to expect are in the 24 to 30 gph range cruising between 23 to 26 mph and rpm around 2700.

Thanks very much for your input SCORPIO.
ps I viewed your pic album and the boat looks very nice. Great work !!