Author Topic: Greetings from Finland  (Read 6438 times)

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Offline Tapani

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Greetings from Finland
« on: August 12, 2021, 08:34:13 AM »
Hello all and greetings from Finland !

Bought my very first motor boat about a month ago - a Jurmo Trimaran from 1971.

Since the boat has - a rather rare thing over here - a cathedral hull and the Finnish manufacturer Tradex had close relations to Glastron at the time I thought I register and join you.

Production started in 1971 as "Tradex Trimaran" with both a HT and a BR version on sale. Even the Finnish president back then, Urho Kekkonen, had a BR to boat guests around his summer residence. Tradex manufactured 15 and 16 foot Glastron boats over here under license at the turn of the -60's to the -70's, haven't been able to find out which models they were..... and discussed the possibilities to produce the Swinger too, but the license costs became too much.

Anyway, I believe my boat was sold in 1971 with a Chrysler 70 hp OB, but never got registered. The last time before first registration in 2018 the hull touched water was early -80's and boat was stored until the owner passed away. At the time it had a 115 V4 2 stroke engine, which didn't run. The person from whom I bought it from swapped the engine to a 80hp four stroke Efi Mercury from 2008, which is quite heavy for the boat, I believe.

But since the boat has not been used much at all during it's life of 50 years it's in rather good condition, I think.

Many things do need attention, but that's part of the deal. For example, I believe the engine sits too low - the bow is very high prior to planing, the ventilation plate runs well under the water at speed, feather spray from the engine too and the boat porpoises quite annoyingly if not fully trimmed down. Loading the bow with a few sand bags helps the slow running position, but not the porpoising at speed.

Let's discuss those items if some you is interested.

A couple of photos attached  8)

Kindest regards from Finland,

Tapani
« Last Edit: August 12, 2021, 08:37:09 AM by Tapani »

Offline Hyperacme

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Re: Greetings from Finland
« Reply #1 on: August 12, 2021, 10:44:45 AM »
Welcome to the forum Tapani !

There's a short Glastron history here ..
http://www.classicglastron.com/gl-reflt-index.htm

Can you post some pictures of your stern/transom/motor/set up ?

Offline dorelse

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Re: Greetings from Finland
« Reply #2 on: August 12, 2021, 11:03:37 AM »
Welcome!!!
1990 Sierra 1700

Offline Tapani

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Re: Greetings from Finland
« Reply #3 on: August 12, 2021, 01:21:20 PM »
Thanks for the replies and welcome  :D

Unfortunately this the only one I have. The AV plate is right at the level of the "keel".

I have a 9 sec video too, but it's too big a file to post.

A few frames - 20 knots speed.

/Tapani

Offline Tapani

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Re: Greetings from Finland
« Reply #4 on: August 12, 2021, 01:22:28 PM »
A few more frames

/T

Offline Tapani

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Re: Greetings from Finland
« Reply #5 on: August 12, 2021, 01:23:27 PM »
And the last one


Offline Hyperacme

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Re: Greetings from Finland
« Reply #6 on: August 12, 2021, 02:43:36 PM »
Looks like a long shaft motor and at level with keel should be good.
New Merc's in the 75 to 115 HP range are about 360 lbs. so not to heavy compared to older inline 6's and V4's which were about 300 to 350 lbs. range.
 https://www.mercurymarine.com/en/us/engines/outboard/fourstroke/75-150hp/

I don't know ..
Sorry if this is dumb questions .. but ..

Have you pulled drain plug and tilted front of boat up as high as it will go .. make sure there's no water in hull under floor ?

Do you have a very large fuel tank and more then one battery in stern ?

Maybe motor is to high and not to low ?

How fast is max speed ?


Offline Tapani

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Re: Greetings from Finland
« Reply #7 on: August 12, 2021, 10:51:38 PM »
Thanks for your reply.

I have an electric pump to empty the hull, not much water there.

Just one battery at the stern, two fuel tanks, 12 gallons in total. One empty last time we tried.

Top speed 33 knots @5700 rpm roughly.... only few seconds to planing. Trimming would raise the rpms.... too high I guess? Should I try another prop first? Maybe a High5? I don't mind loosing a bit speed.

As an absolute beginner: is the motor height setting different with this type of ahull from the norm? Manufacturers recommendatio is spot on with the Merc.

Tapani

Offline Hyperacme

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Re: Greetings from Finland
« Reply #8 on: August 12, 2021, 11:14:37 PM »
33 Knots equals 38 MPH .. which seems pretty good if it's a GPS reading, old pitot tube speedo's can be off.
Your max RPM's as per Merc is 5800 RPM's.

What pitch / brand of prop are you using ?

 

Offline Tapani

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Re: Greetings from Finland
« Reply #9 on: August 13, 2021, 02:00:13 AM »
Hello,

Yes, GPS reading.

First time I checked..... its 854360A45P16 Mercury, so it's a 13.25x16.

Hmmm...... A lot easier to swap the prop to a higher pitch than raise the engine.

Attached is lower boat weight part of the prop table from the factory manual.

For an 18 foot 1800 lbs boat (pay load included) I'd look at a 13.25x20 Laser II, a 12.75x20 Hi5 or a 13.75x19 Trophy.

Most of what we expect to do is two persons, 20-25 knot cruising. And naturally try to get rid of the porpoising and reduce nose lift during hole shot.

As it is now it porpoises almost dangerously (with even a touch of trim from the very low position), massive bow lift during hole shot, it's difficult to steer at speed, pulls to the right and when releasing the throttle it veers strongly to the left.

Any comments and ideas are greatly appreciated.

/Tapani
« Last Edit: August 13, 2021, 02:03:58 AM by Tapani »

Offline Hyperacme

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Re: Greetings from Finland
« Reply #10 on: August 13, 2021, 02:23:53 PM »
Maybe try a few different props
If that doesn’t work maybe try a whale tail
One of those fin things that are attached to your cavitation plate
Some people say they work
Might be worth a try if all else fails

Offline Tapani

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Re: Greetings from Finland
« Reply #11 on: August 16, 2021, 07:35:03 AM »
Hello again,

I found another similar boat with a Honda 90 motor, which sits quite significantly higher than mine - see photo.

I talked to owner and his top speed with four adults and 100 litres of gas in a stainless steel stern tank is 38 knots. He can also make to boat porpoise by trimming the engine up, way up from the 0-position and it will calm down by just tapping the trim a touch down. I can't run anything above max negative.

I will need to drill new lower holes, make an aluminum plate behind and also in front of the transom to beef if up and cover the wrongly drilled holes and the install the engine 2-3 holes higher. This won't happen until next week when I go home from the lake.

After I get this sorted I will address the prop issue.

Tapani
« Last Edit: August 16, 2021, 07:38:02 AM by Tapani »

Offline Hyperacme

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Re: Greetings from Finland
« Reply #12 on: August 16, 2021, 10:04:26 AM »
A motor to high or to low will porpoise ...

Doesn't your motor have a few mounting holes on bracket ?
You could try them first before drilling new holes.

I would epoxy wood dowels into old motor mount holes then cover with gel or Marine-Tex or something to seal holes.
 

Offline Tapani

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Re: Greetings from Finland
« Reply #13 on: August 16, 2021, 10:36:55 AM »
Thanks, yeah it does. Sort of.

The lower ons are not drilled correctly to similar positions as the upper ones. The are much farther than 8". Only on hole can be raised - there's also an aluminum trim on the edge on the transom, adding a plate will be enough for the motor to clear that.

Thanks,

Tapani

Offline Hyperacme

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Re: Greetings from Finland
« Reply #14 on: August 16, 2021, 01:34:04 PM »
I used "CMC Transom Wedges" to get clearance for aluminum trim and so my splash well drain would drain better.

CMC Transom Wedges
https://thmarinesupplies.com/collections/cmc-marine-products/products/cmc-transom-wedges-2-degree

Offline Tapani

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Re: Greetings from Finland
« Reply #15 on: August 16, 2021, 01:46:22 PM »
Great, something like that, but with even thickness for ease of making.

👍

Tapani

Offline thewillets

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Re: Greetings from Finland
« Reply #16 on: October 22, 2021, 09:12:18 AM »
Are you sure that the motor is tilting far enough toward the transom ?

It sounds like the motor when pulled all the way "in" is still to far "out" if you get my meaning.

I met a first timer with an older boat last summer who had a similar problem and his motor had a pin that set how close the motor would tilt toward the transom.  I am not an expert in outboards but I got to looking at the angle and after a bit of puzzling it over I found that pin and moved it 1 hole closer to the transom.

He took the boat out and it made a huge difference.  Just a thought, there are people on this forum much more knowledgeable than me !
1965 Futura 500 V164

Offline Tapani

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Re: Greetings from Finland
« Reply #17 on: June 06, 2022, 06:08:35 AM »
Greetings again from Finland !
 
I know it's been a while, but I've finally got progress with the Jurmo Trimaran 😊

Last summer, I experienced quite a bit porpoising and trimming problems. Now these are pretty much solved ? at least to an acceptable level.

I raised the motor in total three holes and now the anti-ventilation plates sits 1" above the keel line. I had a 10mm thick aluminum plate made to support the transom. I also tried two new props and now I'm running a four bladed Trophy Plus 13 3/4" diameter and 17 pitch. With only two holes up last summer I maxed out 5950rpm and app 33 knots.

I de-restricted the motor to the full 100hp by removing the orifice and remapping the ECU. Now with the motor one more hole higher I just run into the limiter (6120rpm) at 34 knots with two persons and 35 knots alone. The hole shot is the best thing of all, the engine's characteristics improved dramatically. I installed also Vesselview Mobile and a cooling system pressure gauge for some peace of. I will run this prop at least for the summer ? no need to go any faster with a 52 year old boat, best cruise is 21 knots anyways. Fuel consumption is around 3-3,5 us gallons an hour at that speed.

I also re-did totally the electrics and relocated the battery to the front. Further, I replaced the Hydrodrive 90 steering with a Baystar and it made a huge improvement. New bilge pump plumbing, improved lights, swimming ladders and some grabrails and an electric winch for the trailer completed my winter efforts.

Kindest regards,

Tapani

Offline Plugcheck

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Re: Greetings from Finland
« Reply #18 on: June 06, 2022, 08:29:45 AM »
The prop you're now running is providing stern lift, it's what I use to solve very similar issues on a V-8 IO Glastron.    It's amazing how small changes can have such big effects
Michael
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Offline Hyperacme

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Re: Greetings from Finland
« Reply #19 on: June 06, 2022, 02:58:52 PM »
35 knots = 40 MPH
Sound like you got everything sorted out ..