Thunderboat question

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Wayne Johnstone

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Joined
Sep 30, 2011
Messages
657
Hi. Just wondering what size motors you run in your Thunderboat class and if they are stock or can be modified. Thanks
 

FloridaScaleBoater

Well-Known Member
Joined
Oct 2, 2005
Messages
6,054
Hi. Just wondering what size motors you run in your Thunderboat class and if they are stock or can be modified. Thanks
Both IMPBA & NAMBA are stock Zenoah engines The rule book is your friend and answers most questions,


1. CLASSIC THUNDERBOAT


a. Hull Specifications

i) The boat may be of wood or fiberglass construction.

ii) The hull length will be between 48” – 56”.

iii) The hull width will be a minimum of 24”.

iv) The transom will be a minimum of 10” in width.

v) The hull design will only be one of the following types: round nose,

step deck, or chisel nose.

vi) Nothing on the boat may be further than 5 1/4" behind the transom.

b. Motor Specifications

i) Engines must confirm to NAMBA Class G‐Limited specifications, (((see below for engine specs)))


see rule B.3.a in this section.

ii) The pipe and muffler must be inside the boat and exit through the

transom.

c. Appearance

i) The boat must have a sponsored paint scheme with sponsored IDs

and U numbers on the boat.

ii) The boat must have a human driver figure in a front or rear cockpit.

The driver must be a scale of 1/8 to 1/6 in relationship to the size of

the boat and wearing a life vest and helmet.

iii) The boat must run with an engine cowling or dummy engine to cover

as much of the boat’s engine as possible.

3. G‐Limited Class Rules


a. General Engine Specifications


i) Engines will be a Zenoah G260 PUM with no modifications allowed

except those noted below.

ii) All replacement parts must be from the original manufacturer and the

same type engine (Zenoah G260 PUM to Zenoah G260 PUM). No

part swapping from other manufacturers or engine types is permitted.

iii) The carburetor must be one of the following: Walbro WT‐257,

Walbro WT‐644 or Zenoah WT‐1027.


iv) All carburetors will be stock with no modifications other than those

noted below:

(a) The velocity stack/Air Funnel (part #848ES08300) may or may

not be used.

(b) Any type of bolts may be used to mount the carburetor.

(c) The idle stop screw may be removed.
 

FloridaScaleBoater

Well-Known Member
Joined
Oct 2, 2005
Messages
6,054
IMPBA



G. Classic Thunderboat

1. Hull Specifications

a. Boats may be wood or fiberglass/composite type construction.

b. Length shall be a maximum of 56 inches, minimum of 47 inches. Width shall be a minimum of 22 inches.

c. All boats shall have a front or rear cockpit with driver figures from the 1950s - 1970s era, no cartoon or animal characters.

d. All boats shall have a period correct paint scheme and sponsor name & logo. The Sponsor and/or logo may be original or of your own choice.

e. Normal hull configuration shall be conventional round nose, shovel nose, dropped sponson or pickle fork design. The pickle fork shall not exceed 10% of the hull length and be modeled after a classic era boat (1950s-1970s era).

LAST REVISED September 2019 I - 9 Large Scale Gasoline

f. The ride-pad of the sponson may extend up to 1/8 inch beyond the sponson transom. No rear sponson, or other riding surface allowed aft of the sponson transom. Engine belly pans are allowed. Engine belly pans may not extend beyond the engine compartment.

g. Nothing may extend more than 5 1/4 inches beyond the transom.

h. The strut mounting is optional. Maximum strut length of 3 1/2 inches in length and 1/2 inch in width.

i. A minimum 50% of the gasoline engine must be covered with either a cowling or period correct fake engine. This does not include header and/or tuned pipe.





3. Engine Specifications


a. Spec engines will be a Zenoah G260 PUM ONLY.


b. The engine may run a stock unmodified 257, 1027, or a 644 with choke carburetor.

c. No internal modifications are allowed. Replacement parts must be from the original manufacturer and the same type engine (Example: Zenoah 260 to Zenoah 260). No part swapping from other manufacturers or engine types is permitted.


d. The engine ignition coil may be moved to another location on the engine or hull.

e. Each engine must have a working throttle control and the engine must be set up to be completely stopped with the transmitter controls.

f. Recoil pull start must the primary method of starting. EZ Start and pulleys are acceptable.

LAST REVISED September 2019 I - 8 Large Scale Gasoline

g. The top 3 finishers at the annual IMPBA Gas Nats may be torn down and will be checked using the following Specs as listed below. If the engine & muffler is not legal they will be disqualified from the event.

h. All engines & mufflers are subject to inspection at any time during the event
 

JimZaremski

Well-Known Member
Supporting Member
Joined
Feb 17, 2011
Messages
769
RRRick, Wayne is from the land down under.:D
while true, I looked through the AMPBA rule book and they don't appear to specify anything resembling Thunderboat. Since Wayne used the phrase "your Thunderboat class" I assume he wants to know what the rules are up here in IMPBA and NAMBA.

Wayne, Rick has already posted the rules. The key point is that the hull must resemble a 1950s-1970s "shovelnose" unlimited, must be decorated in a period-correct scheme (doesn't have to be of a real full-size boat, just no silliness like color shifting paint or other stuff which didn't exist back then.) Also they must use a Zenoah G26 which cannot be modified in any way.
 

Wayne Johnstone

Well-Known Member
Joined
Sep 30, 2011
Messages
657
Hi all. Yes I am in Australia. There are a number of us here that have an interest in this class of boat and as you have rightly said, we don't currently have a Thunderboat class in our rule book. So I was just enquiring what rules you guys run by. This is the boat I have currently.20190921_182747.jpg
 

JimZaremski

Well-Known Member
Supporting Member
Joined
Feb 17, 2011
Messages
769
Hi all. Yes I am in Australia. There are a number of us here that have an interest in this class of boat and as you have rightly said, we don't currently have a Thunderboat class in our rule book. So I was just enquiring what rules you guys run by. This is the boat I have currently.
Wayne, the NAMBA and IMPBA rules are pretty similar, there are some minor differences here and there. Most notably the min/max dimensions. It is easily possible to build/design a boat which is legal for both organizations. if I remember correctly, Zippkits' first kit (the Rockett) was only IMPBA legal, but everything they've made since (Rivett, Bullitt, Missile) has been legal for both. If you're looking to start up a Thunderboat class in AMPBA you could pretty much pattern it off of either the IMPBA or NAMBA rules and call it good.
 

Wayne Johnstone

Well-Known Member
Joined
Sep 30, 2011
Messages
657
Thank you all. Unfortunately I didn't build this one so can't take the credit but it is a very nice boat
 

Bob Blazer

Well-Known Member
Joined
Jan 1, 2006
Messages
264
Wayne by all means keep them STOCK they are plenty fast the way they are and you will have more fun racing competitively.
 

Duke Mordja

Well-Known Member
Joined
Jan 15, 2005
Messages
622
Nice looking Thunderboat. really like the blower and header pipe details. Makes it look very true to intentions of the thunderboat class.

Where can one get those at??
 

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