Help requested for increasing the knots of speed boats.

Hi every one, we constructed a Fiberglass boat for open sea (not for coast) expecting a speed of 20 knots.The boats length 50.5' X width 13.45' and has a draft of 3.6'(specifically for the sea).Approximate weight of the boat is 24 tons.These boats are fitted with 2 inboard engines of 300 HP each,these are designed to provide 20 knots.In our boat generally the draft is 2.23', to make it 3.6' a skeg was fixed at the bottom of the haul.
Our problem is that these boats does not give speed more than 13knots.I have been trying hard to brainstorm the possible problems for a while now,but no success.If any one has faced similar kind of problem then please advice or any kind of advice or help is truly appreciated.I really need help as its becoming urgent day by day.Thanks for your help in advance.

Regards
sna

 

Can You tell us more about design of this boat, who is the designer? Any pictures? Have You checked actual weight of boat?

 

Hi,thanks for your reply.
Well the designer and builder of the boat is someone from India and he kind of left us with all these problems and never gave us the full design details.I will try to post picture of the boat soon.The approx weight of the boat is 52910lbs.It might vary 3 tons here and there.
Please let me know if this is helpful.Any suggestion is really appreciated.
Thanks
sna

 

SNA,
Assuming you have a fair hull form with no more than a little aft buttock rise, AND assuming you are swinging at least 24" diameter props, AND assuming the boat trims properly at rest, AND assuming hull trim at full power is no more than 3 degrees bow up then;
53k pounds = ~14 knots
59k pounds = ~13 knots
Your statement "might vary 3 tons" is interesting. To identify this problem, there must be no guesses. Need to measure the actual displacement of the boat in trials condition, with all fuel, crew, and other loads in place. Odds are very likely the boat is heavier than you think.
Even if it is not, I seriously doubt you'll ever get 20 knots with 600 installed BHP. You could have one of many other problems as well, but far more detail would be needed to assess. Check engine load percentage at 100% throttle, and compare actual engine RPM to rated max. Should be 98 to 100% load and 10 to 20 RPM over rated max. If you are off on either of these, then you are not getting full power to the water. Regards, Weed

 

To add, engines in India are likely to deliver about 10% less power due to high temperatures and humidity...

 

PICTURES, PHOTOS AND ANY DRAWINGS WOULD BE GREAT AS A STARTING POINT PLUS THE BOAT UNDERWAY IN THE WATER . INSIDE PICTURES ENGINE ROOM AND ANYTHING ELSE YOU CAN PROVIDE !! . love looking at pictures !!!

 

Concurring with notes above, I note that you are stuck precisely on the "low speed side" of the hump speed. And you are expecting a top speed just past the hump. Your hull has a low slenderness ratio (LWL/displ^0.33), which generates a pronounced hump. The drag at hump will be very similar to the top speed drag.

Depending on the dimensioning of the propellers, you may very well have a low thrust situation with your propellers as well. And with a weight of 24-27 tonnes, high bottom loading and 600 hp are NOT enough to give the speeds you ask for.

I would like to have the particulars for the propellers, transmission ratio, aso to give better info. Any scetches or pics of propeller installation would help.

 

Hello , Thanks for all your replies and suggestion.

As I stated earlier our builder(Mr.Peter Valeth from South India) of the boat has just left us after getting paid for the boat without delivering all design documents of the boat and so we are facing so much of problems.He denied to give us design details.That is a different story.

Now we are also working on collecting all details by physically examining the boat.Its embarrassing that right now I am not able to give you further details but your suggestions and hints are valuable.We will try to collect all data and get back to you guys.
Thanks
sna

 

One of these? I know them.
http://www.**********/high-speed-planing-boat.html
You better build a new one; the one You have would never perform.

They also use stolen images of our rescue cat on their web... Adjusted in Photoshop.

 

Alik, I find it hard to believe that they have the balls to put pictures you published in a brochure of a cat you designed. It just happens that it is a cat and the elevations you drew
make it a favorite of mine and make me wish I had your architectural abilities. If that happened here in the US you would make money off this criminal, fradulent deed.

 

Jabiru light aircraft, I feel, may also be a "stolen design" - Jabiru is an Australian Aboriginal word.

 

In Asia, the only way to avoid damage from stolen pictures is to be two steps ahead of the thief. Clearly they scanned pictures of R38 from our advertisement booklet. But we have new booklet already, and also new renderings of R38 rescue cat

I wonder what they are going to do with those pictures, as they do not have the design. This is type of company I call 'concept hunters' - they keep chasing designers for some concepts/general arrangements for free, then use those pictures for marketing. And if they hook the customer they often hire local draftsman to trace those pictures/GA. I mean even some big companies is Middle East play this way. Our policy is: never provide any usable samples to 'concept hunters', always require pre-paid order even for concept design.

 

Hi snaboats,

Seems the forthcoming advice may never be very helpful...

I was last in India in 1997, and the name rings a bell... My wife was introducing me to her country... With a fellow Rotarian we visited one boat builder who was making "traditional style" lifeboats in grp, and he was proud of the "heft" and thickness of the epoxy (some 2 or more inches thick), and I saw no cloth or other reinforcing showing the test facility (to drop the boats 60 feet into water) ?...

I walked away without comment, not wishing to embarrass my host - who was taking me to all these places and showing me around...

Interpreting Alik's and others comments, may I, - with tongue firmly planted in cheek, - suggest a length or rope and a chart of rope knots, practice that craft and festoon the results all around the boat then you will have lots of knots (sadly not quite what you requested - knots measuring improved velocity of your boat.), - but never the less, - approaching something affirmative... ???

 

OMG, ya thats the one ***** ******,its the same person same address on the site,I just can not believe he is famous fraud internationally.He really cheated us so much that we are really in a pathetic position.Initially he was such a gentleman as the time passed we experienced all his nasty reality.I wish we could have sued him,but suing in India is like investing a big money and time in terms of years.We can not afford to spend money there as it is we have spent a lot on the boats.
I hope we overcome our situation somehow.In this economy its already hard for small business to survive and when you get cheated it makes the struggle more harder.

I will keep in touch with you guys.Thanks a lot for the inputs.

sna

 

How did you build it without having the full design details?

Would be interested to see some photographs of the boat in question at least if lines can't be posted.