Duane, Dawn,
Sam, Nick, and Mike
(Jessy and Jenny)

Home Up Family Pictures Music



Logbook Day 108

Testing the New Motor
Lake Washington

Newport Shores

We dropped the boat into Lake Washington on Sunday for a quick spin around the lake with the new motor. It was a windy overcast day with moderate chop but not to many wakes. We were out for 0:48:04 minutes and covered 8.96 Nautical Miles. According to the GPS log the max speed achieved was 21.63 Knots (24.87 Mph) and an average speed of 11.21 Knots (12.89 Mph).

The Tohastu has a 14" x 11" pitch factory prop on it. It's really nice to have the larger diameter prop.

As expected the motor started on the first click. No choke to worry about, no reving with the throttle plate to keep it going as the old one required. Just turn the key and let it run at idle. You can push the key in (what used to be the choke) and the idle rpms go up then down in steps, 700, 800, and 900. It's so nice to have a motor that idles smoothly without a worry of it dying at the exact worst moment as was often the case with the old 50. It's also nice not to smoke and spit oil at the dock like the old one did when cold. No more embarrassing slick coming from our boat.

At idle the motor is much quieter than our old one. Even though this is two stroke it has much less noise and over all the sound is a much deeper throatier growl that speaks to it's much higher power.

Looking at the cowl you can clearly see that this is Tohatsu 70 TLDI on the back of Allegro, but my boats performance might lead you suspect otherwise. Looking through the Tohatsu parts manual you would discover that the difference between a 70 and a 90 is only 2 parts, the computer with it's different programming and the intake manifold. The 3Y7.. 70hp manifold has a insert plate that restricts the volume of air that can pass into the motor, the 3Y9.. manifold does not have this plate. Now in no way am I saying that Allegro has anything but a 70 on back, but boy this 70 runs great and there seem to be some 9's on parts inside the cowl.

We backed away from the dock and idled out into the lake. This is a quick trip and the mast is still in the trailering position. We're light in the tanks with only one of the four 6 gallon gas tanks full and only half full water tanks. Even so, if anyone has ever browsed this web sites list of mods and equipment on Allegro you know that she is not a empty light boat. For this test the ballast tank was empty at all times.

Once clear of the no wake zone we began testing various speeds getting a feeling for which rpms performance levels would work best from a speed, trim angle, and noise standpoint. Even at WOT the overall noise is less and it's lower pitch makes it more tolerable.

We tried to find smooth water but had no luck even around the north end of Mercer Island with the wind coming from the south.

Here are the speeds we measured on the GPS. These are the average speeds of both with the wind and into the wind tests.

RPM Speed Notes
2000 6.2 knots (7.13 Mph) All fins up.
2500 7.0 knots (8.05 Mph) Will be our slow cruise, easy cockpit conversation .
3000 8.4 knots (9.66 Mph) Med Bow Rise.
3500 10.0 knots (11.5 Mph) Will be our medium cruise, Med bow rise, no side spray, autopilot very comfortable steering, easy cockpit conversation.
4000 13.2 knots (15.18 Mph) Bow full up, enough side spray for occasional cockpit droplets.
4500 16.3 knots (18.75 Mph) Fast Cruise.
5600 (WOT) 21.4 knots (24.61 Mph) Some bow drop at 19 knots.

We'll have to wait for a longer trip to get a measure of fuel consumption but I expect to easily out do what the old 50 got. The way it's carbs were set up it dumped the same amount of gas into the motor from 3000 rpm to near WOT. Going 8 knots used just as much gas as 14 knots. The TLDI fuel injection is suppose to be much better at matching the fuel consumed to the rpm levels and should give substantial savings in the low to mid speed ranges.

The bigger prop also proved to be much better in reverse taking a big bite out of the water and stopping the boat quickly. I thought the larger lower unit might provide better steerage with the motor alone, but it doesn't have much additional effect when coasting. I'll still keep at least one rudder down around the docks.

We're very happy with the results and look forward to more great cruising on the newly invigorated Allegro.

Logbook Addendum

Installing the New Motor
The old two smoke 50 get's an upgrade

Lake Forest Park

On May 31st I finally was able to get the boat to Blue Water Yachts and install my new Tohatsu TLDI 70(+) on my X.  I towed the boat to BWY's Lake forest park shop at 9am Saturday morning. I only missed the hidden driveway once.  As I had the arch and the mast on the boat we couldn't back it into one of their bays in the shop.  We decided to do the installation work outside as the weather wasn't to bad.  This required their forklift to remove the old motor and put the new one on.  To use it, Todd had to first install the new parts for the clutch.

It was pretty straight forward removing the old motor and putting on the new one.  We removed the old motor control box, steering connector cable, wiring harness, and battery cables.  We will reuse the two motor control cables.  The tach also has to change.

The biggest pain was getting the connectors on the ends of the new wiring through some of the holes inside the pedestal. My transom access panels came in handy for routing the cables back there.

Once everything was unbolted and disconnected we pulled the old 50 and set it on the ground next to the boat.  We then filled the old holes in the transom well and the outside transom as the bolt pattern is different for the new motor.  We added a thin sheet of starboard over the full area on the outside transom to bring it up flush to the deck lip and to seal off the holes.  This is attached with lot's of 5200 and a small screw until the motor bolts are drilled and installed.  BWY is actually making the transom wedges they are installing on the M's out of the same starboard material.

Once free from the crate the new motor was lifted onto the back of the boat.  We first drilled the upper holes and cinched them up to test for any gaps between the well and the transom. This test of my transom showed that it was nice and solid unlike some X's that have a internal gap that makes them a bit squishy.  We then drilled and installed the lower bolts.

We discussed transom reinforcements, and I feel comfortable that none were needed. BWY has put motors on over 1,000 Macs and does not feel that they are required. To use their words, "There are other parts of an X hull that will break long before the transom". We installed the motor as normal just using the very large fender washers they use to mount the bigger engines on M's today.

We also installed a BWY steering disconnect system to allow the heavier motor to be unhooked from the rudder steering and locked down straight ahead. After some discussion I also decided to install a separate starting battery as my mains are 2 - 6v golf cart batteries which don't like to give out short term bursts of high current.  We ran new main battery cables from the Tohatsu harness to the new battery which is back in the traditional location aft of the galley.   I'll be installing a combiner and hooking up the 2nd output from my shore charger.

Once all was connected we hooked up the water hose and fired her up.  The motor started on the first turn and ran smoothly with a nice low throaty sound that clearly speaks to the extra power.

The Tohatsu fits very nicely on an X still leaving plenty of access beside the motor. It looks great, sounds great with ear muffs, and will be a great addition.


























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