Restoring the Mark 1 to Jet power.

[luigisante]

A few years ago, I had completed most of the structural work on my boat and was ready to tackle the cabin. My Mark 1 was originally fitted with a 28 H.P. Rotax engine and a UA Jetdrive. When I looked up the original owner of my boat, he sent me a load of original paperwork. Included in that was correspondence between the owner and UA. The Jet Drive appeared to be better at generating galvanic electricity than propelling the Telstar. By the time I got it, my boat carried only the scars of the original drive and a hastily configured outboard mount.

Since I was trying to keep the boat as close to origianl as possible, I had considered replacing the UA drive. I found an old Rotax 303 engine and had the original drive which had been left in the boat. Gone were the thru hulls and motor mounts. Thus, if I wanted to install a motor and drive, I would have to start from scratch.

A guy named Larry Pullon came up with the idea of canabolizing old jetskis to convert small jon boats to jet power. Larry cut out the portion of the jet that had the motor mounts and thru hull as well as the mounting hardware for the jet pump. It worked very well in Jonboats.

I decided to have a go at converting my boat back to original jet power using Larry's concept. To his credit, Joe Siudzinski told me I was crazy. In hindsight, he was right. He always told me that I appeared to like boatbuilding more than sailing. He was probably not too far off. Actually, with the constraints on my time over the past few years, I have had little time for sailing, other than beach cats.

Anyway, I cut a huge gaping hole in my boat to accomodate the canabalized Waverunner that I bought and cut down the waverunner to fit. There, the project has sat. I recently started back on the boat and last weekend finally trimmed the waverunner piece to fit snuggly into the aft of the Telstar. The insert only needs minor adjusting (which I will do by wedging the molding in place with foam) and I am ready to glass it in.

I tried to upload a couple of photos but they are in the 500k range. The program says they're too large. Anybody know how I shrink them?

I am so glad to see this part of the project nearing completion. I think the rest of the refit should fall in place easily due to the fact that I have only cosmetics left.

Lou G.

[Ron]

Lou -

Joe is right about the jet-drive. Tony was thinking about doing a 50hp version on the new boat but correctly gave that up. I've got a SeaDoo 20 foot jet-boat with a Mercury 250hp EFI motor and I never really liked it. It's very quick and can do tight figure-8's at speed, but low speed manuevering is almost non-existant. Having a rudder in back may help, but the Telstar is much better off with an outboard that rotates with the tiller / rudder. Not sure if the older boats had the linkage, but it's easy to do it yourself if needed. I had a wing keel Catalina 250 about 2 years ago where I connected the rudder with the Honda 9.9 frame, using a stainless steel rod and rod-end bearings.

You can shrink any photo with most photo software (such as Adobe, Microsoft Digital Image, maybe even Paint. Just reduce the size and / or the resolution and the file size will shrink as well. If you want to stay the same size or go larger, sign up with one of the photo saving web sites (like Photo Bucket) and put the link(s) into the message. It's usually handled as an imbedded IMG command, but the URL should work as well.

[trashpad]

I would love to have one of the roster tails shooting up. I always wanted to glue a bent tube on the transom of the amas to get one.

[luigisante]

Here is a picture of the waverunner cutout in the aft end of the Telstar ready for final fitting and glassing.

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*Edits*

I added a side view of the fitting after the molding had been adjusted a bit. You can see it starting to fit better. The main tasks are to place the thrust line on the centerline of the boat and to deflect the pump exhaust down about 5-6 degrees. The last picture is taken from the engine compartment down. You can see how well the insert fits in the old engine compartment. There are still two issues that concern me - first is the depth of the cockpit. It might interfere with the engine installation in the front. Second is the restricted amount of space in the compartment beside the engine because of the room needed for the header and exhaust. By my rough estimates, It looked like the engine will fit and the exhaust will fit as well.

Lou

[Pat Ross]

Remarkable, looking forward to your launch.

Pat

[luigisante]

The final jockeying of the waverunner molding is done. I have established a centerline and attempted to set the water jet exhaust at a 6 degree downward deflection.

The molding is tabbed in place and ready for glassing inside first.

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I should have the inside glassing roughed in by Sunday.

lou g.

[Pat Ross]

Lou,

Great photo. Tell me are you expecting the boat to motor faster than hull speed? I ask this because I am in the midst of consideration of a new or at least different outboard. The boat came with a 1977 15 HP 2 Cycle Evinrude. It does not function and I am having someone take a look at it this week. I was told because the boat does NOT have a planning hull that the size of the engine will matter very little, regarding motoring speed, after about 6 HP for this particular boat. I was also told that a larger engine would cause the stern to squat more as you tried to increase motoring speed with a larger engine.

I know part of the reason you are doing this is to return your boat to a similar motoring system that it started with, but I am interested in your expectations of how she will motor and what smaller or larger outboards will do for this design. What are your thoughts on this?

Pat

[luigisante]

Why don't you ask a hard question (lol).

The short answer to your question is "I don't really have a clue" but here is my understanding of the hull speed issue. Most of what i know about hull physics (the total of which you could stick in a shotglass and not fill it) I learned from reading "Low Resistence Boats" by Tom Firth Jones. If I understand his explaination, he says that the golden ratio of 1.3 times the sq. root of water line length as the limits on hull speed and wave-train effect do not apply to multihulls. Trimarans even more so than catamarans. The hull speed limitations are associated with displacement hulls. Multihulls are not displacement hulls. The 8-1 ratio of most trimarans and the low payloads of multihull designs makes them easily escape wave train physics. Under sail power alone, multis escape hull speed and, properly rigged, can sail at 1.8 to 2.0 times hull speed. Even a low wetted surface canoe can go 1.8 times hull speed under paddle power alone due solely to the narrow-long hull design. With enough power added, speeds 2.5 hull speed can be achieved. I think the concept of hull speed as a limitation looses its force when discussing multis. I would guess that the physics are closer to semi-displacement or planing hulls than displacement boats.

The original Telstar was powered by a 28 h.p. Rotax engine and a "hands-on" review that was published at the time the boat was being introduced in the 70s, indicated that the boat topped out at 9-10 knots under Rotax jet power. Pictures in the original brochure show the boat riding properly under power so I'm assuming that the transom did not dip as the power increased.

The waverunner I cannabolized was a 3 seater - 55 h.p version. Thus, I'm increasing the h.p. of the original jet drive's engine by 27 h.p., nearly doubling the horsepower and keeping the weight the same as the original engine/jet drive. I expect that I can tweak the speed a bit more. I'm hoping for 10-12 knots. The boat's original molding did not have a lot of downward deflection and the angle of thrust was nearly the same as the boat's waterline angle. The jet system installed in my boat was designed in 1969-70. Waverrunner units have evolved with a bit of downward deflection of the thrust line to counteract the bow's tendency to come out of the water. I have tried to duplicate this as much as possible in my installation.

Finally, I am considering replacing the impeller with one that was designed to tow skiers on a waverunner. The prop is designed for max torque rather than max revs. This might help push the extra weight of the telstar and, like adding gear reduction and larger props on a standard power boat, make the boat's top speed available through a wider weight range.

Anyway, these are my thoughts. Note my disclaimer in the second sentence - I'm guessing and don't really have a clue. I'll let you know the first time I fire up the engine on the Delaware River and go through the boat's sea trials (hopefully next April).

Lou

One last thing. Joe Sidzuinski (who is a true guru on the 8 meter) loved his 9.9 Yammaha high thrust 4 stroke with a 3-1 gear reduction. Others used 15 horses but I think the Yammaha was a detuned 15 horse engine block. He cruised with that engine at 6 knots and burned .35 gal per hour.

[Ron]

Lou -

You're on the right track. Hull speed is a calculation for displacement hulls, and most multihulls are not that. Actual speeds of 3 times hull speed (or more) are possible. For example, the Telstar 28 should do around 6.8 knots. I've done over 15. For an extreme example, the new America's Cup BOR90 (renamed USA) 90 foot trimaran should do around 13 knots, but it has already broken 50 (in 19 knots of wind !!!!!). That's approaching 4 to 1. I'd love to get a ride on that thing.

I also think you'd be better off with an impeller that favors torque over hp. I replaced the stock prop on the 28 with something similar with good results - to push more water but at a lower pitch. The stock impeller on that jet drive is expecting maybe 1,000 pounds of weight. Your boat is significantly more. The pitch should probably be reduced to compensate.

[luigisante]

The best laid plans of mice and men oft go astray ... Steinbeck.

I decided to dry fit the pump and motor this weekend before I glasseed in the waverunner molding. Lo and behold, the engine did not have enough clearance under the cockpit. Luckily, I was able to adjust the opening by removing the back 6 inches of the original molding.

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I had left the small part of the original molding to make sure I have enough room between the pump nozzle and the rudder but the room is needed inside. I'll deal with rudder clearance when I get to it. The molding now goes all the way to the end of the stern.

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because I was so close to the transom, I was able to better measure the opening and the molding and was able to trim the parts to make a closer fit. It is nearly seamless now.

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So, a brief delay may work out to save a lot of time molding the hull/engine together. I am shooting for this weekend to have it roughed in.

Lou Giansante