I am wondering about my hull shape speed wise

Discussion in 'Wooden Boat Building and Restoration' started by sdowney717, Jul 6, 2015.

  1. sdowney717
    Joined: Nov 2010
    Posts: 1,134
    Likes: 73, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    My boat Egg Harbor 37 from 1970, I left off the trim tabs (since they needed repairs due to holes) and it cant get out of it's bow wave.
    I plan to put them back on, they are 36 by 9 inch Bennet's.

    Years ago my Palmer 392's were able to push the hull to 18 knots with the tabs on the boat. The engines are supposedly 265 HP. Today, I cant get above 12 knots and when I try, the bow rises way up and the stern goes way down, and it throws off a huge wave in the back.
    Props are 22 by 20 three blades.
    The hull is like a lobster boat, so how fast should it go, what was it designed to run at you think? Will leaving off the trim tabs affect the boat that much?

    Here are some pics. Is this a semi-displacement type hull?

    [​IMG]

    prop size
    [​IMG]

    [​IMG]


    Deadrise seems to be at most 10 degrees back here
    [​IMG]

    Mid hull
    [​IMG]

    bow front after hauling out
    [​IMG]

    Someone told me if I had an extra 200 HP, like 350HP twin inboards, the boat would do mid to upper 20's?
    I dont have much experience regarding any such thing. EggHarbor built these with a slight hook back aft, so hull does not run perfect straight from mid hull to the stern. The hook is about 3 foot forward from the transom.
     
  2. Ad Hoc
    Joined: Oct 2008
    Posts: 7,276
    Likes: 1,165, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    I don't know much about these boats but...

    What you are describing is a symptom of 1 of 2 things, or possibly both.

    1) Your boat has grown in weight of the years. As such its power to weight ratio has reduced. If your vessel has grown in weight the simple fact is it gets harder to push. Most notably when you approach the main prismatic hump. This is the region just before and just after planing of a hulls resistance. If the weight has grown too much you no longer have sufficient power to drive through this hump, or increase in resistance. Even though you may have sufficient power for top end speed. Think of it like trying to go up a very steep hill in a car. Your car may be able to go 100mph on the flat, but going up a very steep hill from a standing start....not so.

    2) Then the all important length-displacement ratio. Ad noted on a previous thread here.

    As you can see from the graph in the link above...with increasing weight , on the fixed length, the resistance increases. The main hump is clearly shown for the very heavy boats.

    So, if your boat has grown in weight, (or engine lost some power) your boat will struggle to get over the main hump. Effects on the boat at this juncture are: big squat with a large over all trim - will feel like she is going ballistic - and big waves at the bow and stern and unable to plan.
     
  3. sdowney717
    Joined: Nov 2010
    Posts: 1,134
    Likes: 73, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    17,000 something pounds is supposedly what these boats weigh. Draws about 3.5 feet.

    A friend at the marina here just bought one that has Chevy 454 with 340HP each. The seller told him it will do mid 20's. Although it was heavy fouled on the props and Malcolm said he could not get more 8 knots from it. He got it in Long Island and ran out of time bringing it back it was so slow. So it is moored somewhere in Maryland and I guess it will arrive next weekend.
     
  4. Ad Hoc
    Joined: Oct 2008
    Posts: 7,276
    Likes: 1,165, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    Ok lets look at some basic number.

    Looking at the companies published data specs on the boat here:

    A waterline length of 11.40m and a displacement of 11.70tonnes. So how does this sit with reality? Well, looking at a simple hp/tonne chart versus speed length ratio (speed-length ratio in imperial units so you can understand a bit easier), here:

    Hp-tonne chart.jpg

    With 265hp = 530hp with 17000lbs = 7.70 tonne you get around 69hp/tonne. This equates to around 4.2 S/L ratio which translates into 25knots.

    So either the power is incorrect the weight is incorrect or there is something on the hulls bottom plate that is creating some drag. Since whilst the hp/tonne chart is a very rough first hit guide...it is never far out from reality. In other words you're only getting 12knots. That is a S/L ratio of just 2..which is a hp/tonne value of around 18. And if your engines are producing 265hp..that works out at 29 tonne displacement!!

    Thus something is not correct!

    EDIT - UPDATE

    Ok...found this.

    They quote a 2 x 480 hp version doing 40mph = 34.7 knots. So that is a S/L ratio of 5.7. So, if i extend the curve above, now shown below:

    Hp-tonne chart-1.jpg

    This gives roughly 95 hp/tonne....so with 960hp..this equates to roughly 10.1tonne or 22,000lbs.

    This stacks up.

    So, something wrong with your values???...or you have something seriously wrong with the boat that is not clear.
     
  5. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,033, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    What used to happen to boat speed when the tabs were not deployed in the past ? It seems that you will have to re-fit them to at least test whether they make the difference. Have you swapped engine power since ?
     
  6. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 490, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Judging be that run on that boat, it's not intended to go much better the low to mid 20's.
     
  7. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 255, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    I am afraid it is not the same model it used to be in the 70s: http://www.eggharboryachts.com/37_detail.shtml

    Their current 37 is a hard-chine, high-speed boat, so the speed-weight data is not applicable to the one in the OP... ;)
     
  8. daiquiri
    Joined: May 2004
    Posts: 5,372
    Likes: 255, Points: 93, Legacy Rep: 3380
    Location: Italy (Garda Lake) and Croatia (Istria)

    daiquiri Engineering and Design

    Found this page where a person claims that the 37' model weighs roughly 26.000 lb: http://www.uship.com/shipment/1970-Luxury-37-EGG-HARBOR-Sedan-Bridge-C/607951906/
    So, who is right there? A reliable data is needed in order to assess the situation and give you a useful answer.
    • At 17.000 lb (7700 kg) and approxim. 10.5-10.6 m LWL you boat would have approxim. 5.5 slenderness ratio
    • At 26.000 lb (11800 kg) the SR is only approxim. 4.5
    That's two different animals - just check the two resistance curves (red and green):
    SR.gif

    In the last picture in your opening post, your boat is lifted by a gantry crane. These are usually equipped with the load display, so the crane operator can measure the weight for you. Let us know.
     
  9. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,033, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Looking at all the barnacles on the bottom in the picture, hardly surprising it lost a few knots !
     
  10. sdowney717
    Joined: Nov 2010
    Posts: 1,134
    Likes: 73, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    There are no barnacles on it today and it is in the water now with a clean bottom. The last photo, showed it when hauled out to get new bottom paint, etc...

    The boat lift has no weight gauge.

    Motors are the same ones. It certainly is possible the motors are not producing their rated power, they are old, they dont smoke and the compression is within the normal range.
    The only difference I definitely am aware of from when the boat was able to run faster and today is I left off those trim tabs.

    I dont run this boat at high speeds, I have always run it slow like 6 to 8 knots, so I dont have a lot of higher speed data in my experience with it.

    When I said it did 18 knots, that was about 10 years ago, right after putting the boat in, and I got that speed number from the fish finder paddle wheel, so it could have been faster.
    I still remember it was effortlessly moving fast then when i WOT tested it.

    Before when going fast, I can recall seeing the transom clear of water, and was able to see the trim tabs. I never actually moved the tabs. Would having tabs just straight back make such a difference?

    Also the boat is running E10 today while 10 years ago was running pure gas. E10 has less energy so the HP will be lower. I seem to recall it was able to easily do that 12 knot figure, and today it struggles with bow going way high and stern digs down low and throw a huge wave, it did not used to do that at all. I seem to recall when it sped up there was a fairly smooth speed up with not much attitude change to the boat. I do remember the boat motors back then could only get to 3500 rpm when they were rated for 4000 rpm.

    Today , if I push the motors up, the port engine got to 3500 rpm and the starboard to 3000 rpm and that was the max they could do with the hull collapsing in the back, bow way way high and huge wave you could surf ride on and the GPS says 12 knots.
     
  11. sdowney717
    Joined: Nov 2010
    Posts: 1,134
    Likes: 73, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Finding info on weight, here someone says their aft cabin model is 20,000 lbs.
    http://www.network54.com/Forum/9797/message/1041182755/Your Question Re Fuel Consumption

    Mine should be lighter since there is less structure in the sedan cruiser version.
    Hull is about 1 inch mahogany, about 13 feet width, 37 feet, oak frames are about 2 1/4 inch by 1 1/4 inch and spaced on 9 inch centers with the oak keel underneath.
    Other people have told me 17,000 lbs thereabouts.

    I found an archieve of a dead site showing various engines and props and speeds
    https://web.archive.org/web/20121110191832/http://eggharborowners.org/

    Mine are Palmer IH392 with 2.57 to 1 gear reduction velvet drives. Reported speeds are about 20 in the list.
     
  12. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,033, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    Could it be one of your engines is down on power for some reason ?
     
  13. sdowney717
    Joined: Nov 2010
    Posts: 1,134
    Likes: 73, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    Certainly is possible.
    One reason I don't try to go fast is to use less fuel, but I do want to keep the boat in good running condition.
     
  14. sdowney717
    Joined: Nov 2010
    Posts: 1,134
    Likes: 73, Points: 58, Legacy Rep: 274
    Location: Newport News VA

    sdowney717 Senior Member

    I forgot, there is one thing I changed on both engines.
    I never liked the 4GC Rochestor carbs on the engines. They had issues, like heat soaking and when the boat rocked, their huge fuel bowls sloshed fuel so much the motors would cut in and out as the jets would get uncovered (my theory)

    So i pulled them and put on marine Quadrajets from chevy 350 engines.

    It may be I have set them up too lean on the primary jets.
    Someday I will get in there and adjust the power piston up so it will run richer mixture, or increase the main jet size.
    Going from 350 cubes to 392 cubes, the engines would need about 10% more fuel flow I think.

    If the fuel mixture is too lean, the engines will bog down under load, which I think now is what is happening maybe...
     

  15. Mr Efficiency
    Joined: Oct 2010
    Posts: 10,401
    Likes: 1,033, Points: 113, Legacy Rep: 702
    Location: Australia

    Mr Efficiency Senior Member

    You have to think it is engine related, given that everything else seems to be in order. Or as before, anyway.
     
Loading...
Similar Threads
  1. boony
    Replies:
    6
    Views:
    175
  2. WhiteRabbet
    Replies:
    10
    Views:
    269
  3. Josh Goodswen
    Replies:
    31
    Views:
    1,386
  4. Joe Earl
    Replies:
    6
    Views:
    1,247
  5. Travis Grauel
    Replies:
    10
    Views:
    2,675
  6. AAnderson
    Replies:
    5
    Views:
    1,377
  7. Floatything
    Replies:
    0
    Views:
    1,704
  8. Rollbar
    Replies:
    12
    Views:
    2,580
  9. Insomniac
    Replies:
    49
    Views:
    4,457
  10. buzzy bee
    Replies:
    11
    Views:
    2,541
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.